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Diablo 4 will let you play as a demon
Check out these videos. It would definitely be a fun prospect to play as a large demon. The character could either be a demon not allied with hell (the demons involved in the creation of the Nephilim were separate from the rest of the demons) or somebody who became like that following a deal with a powerful entity. It would definitely go well with the below suggestion that Diablo 4 will have you fighting angels. To mix it up you could have a prologue where you play as Diablo himself. Matti 23

The enemies of Diablo 4 will be Angels, not Demons
Heaven will declare war on Sanctuary, as humans are growing strong enough to pose a threat. The demons may attack as well, but they will not be the main focus of the game.
  • What makes you think you won't be fighting Angels in Diablo 3?
  • Apparently this was originally going to be the plot of Diablo III but was scrapped early on, as a game set in heaven seemed "too different" from it's predecessors.
    • However, the final act is set in the High Heavens, as they're being invaded by Diablo's army. And there's the question of what would the expansions bring.
  • Slightly confirmed, as Malthael becomes evil in Reaper of Souls

Dark Wanderer is Leah's father
We know Adria was her mother and a great warrior who was lost when Tristram fell to the demons was her father. This warrior was going to become or was already the Dark Wanderer.
  • An entry from Adria's journal as seen in the beta seems to confirm this
  • Makes sense when you consider that it's heavily hinted that Diablo will possess a female host this time, most likely Leah and that previously, everyone that Diablo has possessed is descended from King Leoric - the Dark Wanderer who was the warrior from the first game has been confirmed by Blizzard to be Aidan, the eldest son of King Leoric and Albrecht's older brother.
  • Confirmed.

Tyrael has gone rogue in D3 (added before any news released)
Either by taint of the World Stone, always rogue or having to flee heaven, Tyrael is now a rogue Angel. The first is obvious, and the second and third have evidence. Tyrael was the deciding vote on leaving Sanctuary in existence. He created the idea of using the soul stones on the Three Prime Evils. Then he destroyed the world stone after his soul stone idea fell apart. Either it was all part of an "evil" master plan or heaven will thing it was.
  • Confirmed, to the extent of going rogue. He gave up his angelic power and became mortal because he could no long stand by the Council's actions. He's still good though.

Adria will kill Leah and become Diablo's new host
It would be the perfect Player Punch.
  • Far worse, Adria outright betrays the party after Azmodan is killed and forces her own daughter to become Diablo/Tathamet incarnate.

Leah is currently possessed by or is Belial
Got this from a mix of the Black Soulstone trailer and the Book of Cain. In the Black Soulstone trailer it doesn't really make sense if Azmodan is talking to Leah. Either Leah's dreaming herself in the place of someone else, or Azmodan's talking to someone inside Leah. In it Azmodan talks about traps and deception, which is the providence of Belial.

Additionally, in the Book of Cain it says, "[Belial] is often trapped within the intricate webs of his own machinations." This could be forshadowing to Belial having taken human form to further his plans and having totally fallen for it himself, Becoming the Mask. He believes his own lie that he is a human woman named Leah.

Most of all, everything is screaming that this game's plot is going to focus on Azmodan and Belial. Leah being Belial or being possessed by Belial would keep things focused. And, well, continuing the family tradition of being possessed by Diablo is just too easy.

Jossed with the revelation that Leah was Diablo's latest anchor, and so an integral part of his plan to become the sole dominant aspect of the reunified Tathamet. Azmodan was speaking to Diablo.


The above WMGs were posted before Diablo III was released.

will be the expansion's Big Bad

The main page likened Adria's treachery to Melissan's revelation of her true scheme in Throne of Bhaal. So, following that plot, it may not be too much to guess that, taking advantage of Nephil immunity to fate, Adria was actually driving the Tathamet into eternal Abyss living quarters while pretending to be Diablo's loyal mistress, intending to take the opportunity to become the new, improved, fate-impervious Prime Evil. You thought the Angels were scared of the reunified Tathamet because the Scroll of Fate dictated who'd win? Well, if Adria pulls this one off, Heaven is going to be completely blind. Of course, there's the problem of where to get the requisite power before Heaven catches on. Maybe it depends on whether Leah's soul is still intact for Adria, possibly having an advantage as her blood mother, to pull in with Tathamet filaments still attached...

Not quite, but she IS a boss critical to the plot of Reaper of Souls - Her death reveals Malthael's location, and she was trying to steal back the Black Soulstone for unknown reasons.

Adria may not be human.
It was noted how little she aged. She produced a powerful daughter. There is one lingering problem with Leah's parentage, though. Who is Leah's genetic father? It is implied Aidan earlier on, but later Diablo is the "real" father. Was this Albecht completely converted into Diablo or Diablo possessed Aidan who was still very human when the conception would have occured? If the former, this takes a hit. If the later, then Leah's powers (while guided to be hellish) would be from her mother potentially. Two possibilities, rogue angel or angel possessed human trying to recreate a Nepheleam as the potential ultimate host for Diablo if the plan worked. They weren't expecting, or this was Plan B if it didn't happen, the world stone's destruction unleashing the nepheleam's potential "naturally". If not an angel, then there is one demon who kind of just vanishes from lore, Lilith, who showed up as a bonus boss in D2. Maybe Adria was/is Lilith?
  • It's not certain what the rate of transfiguration of Aidan's body->Diablo's body was, but I wouldn't be surprised if, anticipating/guiding Aidan mating with Adria, Diablo made priority one the sculpting of Aidan's gametes, so they'd have at least some of Diablo's own aspects in there.

Malthael will prove to have become evil.
Although not necessarily by infernal taint. In any case, not only is Malthael missing, Tyrael feels obliged for some reason to take the post of Wisdom—Malthael's post—after Diablo-Tathamet is destroyed. And it's rather worrying, given that Blizzard is happy to use precepts from medieval Christian lore, how similar Malthael's name is to that of the Goetic demon Malthas (depending on the grimoire you use, you may better know him as Halphas). If Malthael is associated in any way with storks, the favored way for Malthas to manifest, we're going to have problems.

While the demons seen to date are explicitly not fallen angels, Malthael may start an all new sort of demon that is just such a form of malevolent Order. And he did say that he would prevail in the end, no matter what, when Imperius was calling for Sanctuary's destruction. Did the Worldstone's destruction force him to begin an emergency plan to guarantee Heaven's eternal primacy? he a reincarnation of the original Anu, who purged Tathamet from himself and sought to obliterate him, and now is trying to finish the deed outright? Even at the cost of turning Sanctuary into an Eldritch Location by purging all of its demonic-source elements away?

Confirmed in Reaper of Souls

Diablo III will have more than one expansion
At least two in fact, one dealing with Adria as the endboss and the other one dealing with Malthael, who may have turned evil. Both will probably use the Black Soulstone for their aims, prehaps resulting in a new Tathamet being reborn as in the end, while Diablo's body is destroyed, we do not see the Black Soulstone being destroyed. The Adria expansion may come first, given most player who actually pay attention to the lore's urge to kick her ass because of what she did to Leah. The Malthael expansion may involve Imperius pulling a Face–Heel Turn in order to destroy the Nephalem and becoming a major antagonist in the expansion.
  • There's still something left of Imperius? But it's also possible that his battle will end not with his death, but with a Heel Realization that the Nephalem aren't hopelessly corrupt after all, indeed are closer to Anu's true original nature than the angels ever were. Of course, there's an excellent chance he'll suffer another Curb-Stomp Battle if he tries to follow through on Malthasael. As for Malthael's schemes if he proves I spoke of above, maybe him trying to restore and/or become a reborn Anu, even if nothing recognizable remains of the universe in the process?
    • There's plenty left of Imperius. He survived the cutscene just fine, shows up at least twice in the game afterwards and even after Diablo makes it the Pinnacle first, he and his friends are very clearly alive and moving.
    • For Imperius, it could be possible, assuming that he was killed, for his remains to be salvaged and imbued with the Black Soulstone. Think about it the most badass angel merged with the ultimate evil! It would be a awesome battle!
      • Jossed. At least to the extent that one expansion will focus on Adria and one will focus on Malthael. Adria is dealt with in almost an offhand manner, as a stepping stone on the path to taking out Malthael in Reaper of Souls. A second expansion could still possibly be done however, as Malthael shatters and absorbs the black soulstone during his boss fight, and Tyrael mentions that Diablo had been released because of it and is free now.

The Monk's resource: Spirit is actually Spirit Energy aka Reiki
  • This would at least explain what type of Ki he/she is using.

The Real Money Auction House will fail
  • The RMH will not bring in the revenue blizzard expects, people will find ways of duping items, because really you can't stop the playerbase from figure out ways to do it, the economy of the RMH will be totally destroyed by it. Blizzard will flounder and bluster about the online single player being nessecary for several months afterwards until they realize people already have offline server emulators and THEN they will finally give in and stop screwing the player base.
    • Given that the items, like the characters, are actually kept on the servers, duplicating items is going to require server hacking this time. Even if Blizzard's intrusion countermeasures are imperfect, just how many of the earlier duplicators are going to be willing to take the time to hack the servers? It was planned as online-only from the first moment of inception, anyway?
    • Also, considering D3 has become one of the fastest selling games of all time, the idea that Blizzard will need to make money off the RMAH to pay off development is flawed. At worse, you could say that any money Blizzard makes off the RMAH goes towards server upkeep and additional budget for expansions. Mostly importantly, every game fanbase has this sort of reaction to this sort of thing and if it does happen, it's not because the auction house (or whatever) failed but because the game does.
    • Its unlikely that there's going to be an effective server emulation for Diablo III, given that the game client is incapable of running the game on its own. Any work done on creating an unofficial, hacked server is going to require a lot of reverse engineering and guesswork. Still, its entirely possible for a dupe bug to exist in Diablo III, just like there was in Diablo II on
    • Unlike StarCraft II or World of Warcraft, Emulating the server is simply inviable. All of the game's code runs server-side. Reconstructing a server will require the same effort as developing the game again. Hackers who could do that, could as well just start their own game company.
    • Even if it inviable, it is not impossible. Those who are right now working on defeating the DRM of Diablo 3 will persevere, not out of a desire of pirating the game, but because their pride as hackers will not let them give up. A new kind of DRM is seen by hackers as a new challenge that must be overcome no matter what. So, even if it takes them years or even decades, the servers will ultimately be emulated, simply because they want to prove that it can be done.
  • Well, it seems that the Real Money Auction House failed, indeed. But not because it wasn't used. Rather, according to Blizzard, it has failed because people used it too much, preferring to Bribe Their Way To Victory rather than put some effort in finding gear in their games. That's the alleged reason the PS3 and PS4 port of Diablo 3 is not gonna have the Real Money Auction House. So... Confirmed, I guess?
  • Blizzard announced in September 2013 that the RMAH will close in March 2014.
  • As of April 2014, both Auction Houses are closed.

Leah's resurrection will come about due to Tyreal... because he's fallen in love with her.

Azmodan is in fact the greatest tactician among the lords of hell, because the standards in heaven and hell are very low
Being a skilled commander needs a number of qualities (ability to motivate your own forces, quickly see and respond to opportunities, have a good understanding of everything involved in the battle, etc.). Looking at the different qualities embodied in the archangels and major evils, the personalities and skills that would lead to these qualities are split between the angels and demons, thus, none of them would make a very good commander by human standards. Humans, who combine qualities from both Angels and Demons, have the potential to be much more tactically skilled, but against swarms of much more powerful demons or angels, this wouldn't matter much.

A future playable class will be bard
The terrible, Canon Discontinuity Hellfire expansion for Diablo had three new classes: monk, barbarian, and bard. As of Diablo III, two of those are playable. In Act 1, at the inn, there is an NPC fixated on having a bard around to lighten the mood for everyone. He then decides that he will write the song about the (latest) downfall of Leoric himself, plus or minus trivial matters like truth getting in his way. The fact that the player character is a Nephalem lends credibility to the awesome power of BARDS! vanquishing evil with music.

The next playable class will be Paladin
As of now, Diablo III has two melee classes and three ranged ones. Of these, two use Intelligence as their primary stat, two use Dexterity, and only one uses Strength. Therefore, the next class will be a Strength-based melee class. And given Blizzard's prior records, Paladins appear to be the most likely candidates for the position.
  • Sorta-confirmed, the Reaper of Souls expansion has a paladin-esque class, the crusader.

Malthael will become the Expansion's Big Bad.
During the events of the game, Malthael did not appear as Tyrael said that he has gone mad. This probably will change the fate of the entire plot and thus he will become a force to reckon with.

The jewel Covetous Shen is searching for is yet another Soulstone.
He says its cursed and has brought doom to everybody who has ever possessed it. The being Dirgest that Shen claims it contains is actually part of the essence of Tathamet.

Sort-of confirmed by Reaper of Souls - the jewel contains the soul of Dirgest, who is the Xiansai God of Desire. We haven't found out what happened to it yet, though.

  • According to Shen's mission, Dirgest has escaped the jewel, and Shen has the jewel in his possession now.

Some of the various login difficulties and balance issues in Diablo 3 are artistic decisions, not mistakes
A lot of the components of Diablo 3 are either updated, or based off of, features in Diablo 2. (The 5 character classes are similar to Diablo 2's non-expansion classes, the locations are similar, the boss spawn system, waypoints, and loot systems are touched up bu the same, the auction house copies D2's trading, etc.) given this:

1. The login difficulties, plus other server difficulties, are meant to mimic the lag, duping bugs, tp killers, etc. dfounds in D2. People on blizzard wanted to bring a similar experience to diablo 3, but did not want to add things that would allow the death of hard core characters. While some lag exists, it has been greatly removed, while these new difficulties allow players to experience the server issues that are integral to the previous game.

2. The balance difficulties (disclaimer: I have only read about large difficulty jumps in inferno, not experienced them, so take their existence with a grain of salt.) are meant to replicate the wildly unbalanced skills of Diablo 2, plus the immunity difficulties. Players don't like to feel that their character choice was wrong, or get stuck relying on someone else for a particular area, so designers simply added large difficulty jumps to preserve the occasional feeling of helplessness and frustration in particular zones, while still giving players an ability to work through it.

Fate no longer binds angels and demons.
The fate predicted by the Scroll of Fate was prevented, or at least changed. This renders its predictions moot and Itherael will have to find a new job. On a serious note, this means angels will begin to be more 'human', now that they may no longer be bound to a Fate they can do nothing about.

The female monk would make a great cheerleader.
We've got spirit / yes we do! We've got spirit / how about you?

The Diablo universe will cross over into World of Warcraft around the tenth expansion
Because the restored power of humanity is just about right for a level 150.

Diablo 3's Whimsyshire is actually the player character's mind shattering under all the stress they've been through with the last four acts.
If one takes a look at Team Fortress 2's Meet The Pyro Video they you see something similar happen with the Pyro character. After 4 brutal acts of fighting countless demons, venturing into the bowls of hell and climbing to the highest reaches of heaven and finally achieving their goal, along the way gathering a few strange items that the blacksmith is somehow able to fashion into a staff, you meet a jovial ghost who sends you into a rainbow colored stream of light. In reality, the player character's mind shatters under the strain of everything they have gone through and the result is whimsyshire. The little flowers? Children. The Teddy Bears? Teenagers. The Unicorns? Adults. The happy clouds? Shopkeepers (Just observe how the player character (in my case, the monk) punches a fist into his hand before pointing at the cloud, at which point it gives up loot.)

Diablo will, over time, become a training dummy for human fighters.
Diablo, throughout the series, has shown a remarkable ability to come back from being defeated. However, after beating him twice now, enough information has gotten out to help future humans know how to handle the way Diablo fights. Over time, as the humans get more powerful, and learn more about fighting Diablo, it will eventually reach a point where Diablo's stubbornness in coming back will be exploited by humans as a challenging, but beatable, method to practice combat skills. (Of course, they will need a substitute human to avoid any possessions, so some flesh golems or summons of some sort will probably do the job.)

The Evils defeated in D3 will be reborn again
Tyrael says that the Black Soulstone is flawed and cannot hold the defeated Evils for very long. According to him it's necessary to defeat them all, bind them in it, and then shatter it as quickly as possible, otherwise their souls will escape from it and they will be reborn again. At the end of D3 we see Diablo's body falling from Heaven and burning up in the process, until only the Black Soulstone is left. We also know from D2 that the only place where soulstones can be destroyed is the Hellforge, so the fall won't destroy the stone. It's highly unlikely that it can ever be found at all, much less fast enough to prevent the Evils imprisoned within from escaping. All the effort of the protagonist of D3 will therefore have been in vain.

Confirmed, at least for Diablo, whose soul was released when Malthael shattered and absorbed the Black Soulstone before being killed by the Nephalem. It seems the other Evils may have been incorporated into Diablo's own soul, so if he comes back, we're dealing with the Prime Evil version.

Kormac will become the new Aspect of Justice
Tyrael left his post to become the new Aspect of Wisdom. That's a vacancy right there. Kormac fights for justice and he fully intends to get it regarding his Order, what they did to him, and their plan to invade Heaven.

Each "Adventurer's Body" you loot... in a location where someone's hardcore character died.

Lilith and Inarius in Reaper of Souls
Leaked images include icons that match the characters. After the creation of Sanctuary and the birth of the first nephalem, Lilith wanted to raise an army of nephalem to conquer both heaven and hell while Inarius feared the nephalem and wanted to destroy them. Considering this, upon her return Lilith would want to stop Malthael from destroying the human race and maybe even side with the player for the duration of Reaper of Souls. It would be a good premise to have Lilith as the new Big Bad when she tries to conquer heaven and hell the way she originally intended to in the second announced (but unnamed) expansion. After all, we've defeated the sum of all hells and the former leader of heaven, so what else is there than to fight other nephalem?

Inarius left a number of journals scattered around Pandemonium Fortress, but neither appears in person.

Imperius is the Lord of Wrath and will turn good while Covetous Shen will turn out to be the Lord of Greed and be evil
This leaked video implies that Imperius is the Lord of Wrath in disguise and this leaked video makes it clear he lives. This all implies that Imperius is going to be shown mercy after his defeat and will turn good. Covetous Shen seeks a jewel containing a demon... How do we not know he's not after the Black Soulstone and isn't the Lord of Greed? And what's to stop him and Imperius from clashing in their true forms?

The Necromancer from Diablo II will be the Big Bad

Nope, it's just Malthael.

Reaper of Souls will be the Grand Finale for the series
As the Prime Evils are greatly weakened following Diablo-Tathamet's defeat, some dangling plot threads must be resolved (such as Adria's whereabouts and the status of the other five Sin Lords who are possibly fighting each other for the position Azmodan left after his death) — and Malthael will be The Chessmaster behind those threads. And then, in the final battle, Malthael will merge with the Black Soulstone to become a blasphemous amalgamation of Anu and Tathamet, effectively becoming a deity higher than the aforementioned original Prime Good and Prime Evil and the sole supreme being with the power to unmake heaven, hell, and Sanctuary itself.

Malthael does merge with the Black Soulstone, but the powerup is underwhelming - and Diablo's soul has been released with the destruction of the Soulstone.

Reaper of Souls will end in the release of Diablo and the other Prime Evils.
The Reaper of Souls beta has Adria reveal before death that Diablo is returning and it's because of the players. Once Malthael is slain it's likely that the Black Soulstone will inadvertantly be destroyed releasing the 7 Great Evils setting things up for later expansions and the saving of Leah that Metzen mentioned.


In relation to the above Imperius is the Lord of Wrath and will trick us into giving him the surviving Black Soulstone fragment.
Not only do we get a fragment of the Black Soulstone after the first Reaper of Souls boss fight but Imperius has been noted in Storm of Light to want the Black Soulstone destroyed on the Hellforge despite the risk of the 7 Evils breaking out. Add this to Diablo hinting that Imperius is hidng what he truely is and the Valor turns to Wrath part of the Diablo III prophecy we must come to the conclusion that Imperius is one of Azmodan's Sin lieutenants who had infiltrated the Angiris Council under it's leader Malthael's nose and that he was meant to be a backup incase Azmodan failed to defeat the Nephalem and get sealed inside the Black Soulstone.

A lieutenant of the greatest tactition of Hell would be able to time Diablo's arival at the Silver Spire and attack the Nephalem with an army of Angels only to feign weakness when the Angels he brought get shut down by the corruption of the Silver Spire. Once Diablo got destroyed Imperius would find the Black Soulstone and smash it on the Hellforge while preserving it's fragments to use to capture Azmodan's 6 brothers in anticipation of Azmodan's ascension to Prime Evil. Malthael's actions have only ensured that Azmodan would be the ''only one'' to obtain a fragment of the Black Soulstone due to it's destruction in the Malthael boss fight.

Imperius is actually the Archangel of Wrath and the Sinlord tied to Anger is the Lord of Anger.
Blizzard has stated that only the Fate part of the End of Days prophecy has been fulfilled so the Valor shall turn to Wrath actually refers to the increasing apparency of Imperius's true nature as the Archangel of Wrath(Diablo points out that Imperius hides his Wrath out of fear which isn't Valorous/couragous) and not the Archangel of Valor(there probably isn't one to begin with). The Sinlord tied to the Deadly Sin of Anger which is sometimes known as Wrath will be called the Lord of Anger(the word Wrath is usually treated as more righteous than Anger).

Expansion pack #2 will be set in Skovos (among other places) and feature not only Diablo, but also Mephisto and Baal
All three Prime Evils have their audiologs in Reaper of Souls. Those could be found in Battlefields of Enernity, and they both have portraits and voice actors already. Skovos is mentioned in Adventure Mode by Lorath Nahr and its artwork was shown before the original game's release. At very least, Baal and Mephisto will have more audiodiaries in future expansion.

Expansion pack #2 will have Imperius and Tathamet as bosses
They are the only charaters that haven't been defeated thus far, and both are integral to story and universe of the game. The Nephalem may have to end the Great Conflict of Heaven and Hell by slaying Heaven's champion, Imperius, who will wage war on demons in Sanctuary, causing a lot of destruction, and later the reborn dragon Tathamet, who will be sitting in the heart of Burning Hells. That would be a true Grand Finale!

Tyreal will turn against the Nephalem at some point.
In the Reaper of Souls finale, his narration mentions that, having defeated both Heaven and Hell's champions, the player has the potential to doom them all if they ever fall to corruption. In one of the following expansions, it's highly likely that he will become convinced (whether justifiably or through being deceived by a third party) that the Nephalem have become corrupted and will attempt to bring them down to prevent them from threatening the world. At which point we might be forced to kill one of our greatest allies throughout the series.

Azmodan's lack of tactics and belial's more obvious than expected trickery represent the nephalem's powers

Belial actually was performing a skilled deception, and Azmodan was actually using good tactics against your characters. However, the nephalem's powers, in addition to making them strong fighters, also make them smarter, more skilled, etc., and allows them to see through the lies, and understand the tactics much better than most others could. Since this is hard to show in game, blizzard instead made a stylistic decision to show Belial using a somewhat more predictable trick of simply pretending to be hakaan, and Azmodan as simply throwing soldiers at the fort, and telling you what to do, as a way of showing your character's advantages in these areas.

Reaper of Souls isn't over and the upcoming patches will include Imperius and the Dirgest as bosses.
The game will cause events where the player must first deal with Imperius and afterwords the Dirgest will bind the soul of Imperius to the last surviving remnant of the Black Soulstone and later move to kill Itherael and steal his soul than later claim the soul of whoever the current replacement of Malthael created by the Crystal Arch is forcing the player to kill the Dirgest which would lead to Fate lying shattered forever like in the prophecy.

Imperius's corruption will not go as expected.
The Archangel of Valour will become... The Archangel of Velour!
Imperius: "Tyrael, darling! What do you think of my new outfit? I feel fantastic!"

The next game's plot...
Will involve Angels under Imperius reaching the crossing point that the new heroes (it's a tradition, new game features new classes and heroes) will tell both Burning Hells and High Heavens, in a similar fashion of Conan: "If you keep bullying us out thanks to your bullshit standards... then to hell with you!" and proceeds to initiate the destruction of High Heavens and Burning Hells, leaving Sanctuary alone and people who die there would instead be subjected into The Nothingness After Death, nobody goes to heaven or hell anymore, but in the end, Humanity gets to be free and choose their own path, and if they want faith, there are still other deities to pray at such as Bul-Kathos or Akarat.

More sympathetic Angels like Auriel would also jump ship and turn themselves into mortals, like Tyrael, before it's destroyed.

Tyrael's human face is modeled after the D2 Paladin

Both of them are bald black dudes, and judging from Tyrael's usual tendency to be impressed with humanity, it might not be a surprise when he broke away from High Heavens, he just picked a familiar face based on his experiences to shape his head, and he chose someone that was helpful from him: One of the heroes that defeated the Prime Evils. He picked the Paladin, who's more likely to take on leadership roles.

As of why he might have lost a mustache or something... a small missed thing.

Anu is not as Good as his title (God of Good) suggests

We were never told if he's benevolent or not. What's known is that he wanted to purify his own body from all evil to attain the perfectly good body, thus it gave birth to Tathamet and they ended up duking things out.

Meanwhile, some Angels, the bad ones, like Imperius and Malthael, who seek a more perfected world and has an intense dislike to anything with demon blood in it. What's to say that they got that trait from Anu himself, who wanted a state of complete purity? Meaning that if, for example, Imperius is a gigantic asshole, that trait was sired from Anu who only wants perfect things and not even bothering with the balance. All these demon hating that extends to hatred to humans/Nephalems can be traced back to Anu, meaning that perhaps in the sequel, Anu would be reincarnated like Tathamet via Diablo, and proceeds to say that Nephalems and Sanctuary are not pure good because of having evil's essence and want obliterate it.

Adventure Mode is being used to wrap up storylines without cramming too much into the next expansion

Because let's see, a lot of the follower quest, particular Lyndon and Shen's are still unresolved. What's more is that all the seven evils were released and there are still 5 lords of sin unaccounted for(through it's quite likely that the five would be saved for Diablo 4). Furthermore, Baal and Mephisto have both concept art and could be found in rare lore audios. I think it's likely that, as Blizzard is planning to resolve the storyline started in D1 with D3, that adventure mode-only areas and dungeons is a good way to deliver content without a full expansion. That way a lot of space could be covered without needing to spend too much time producing expansions, and we could deal with some of the Seven Evils without needing to wait for an expansion, which would most likely deal with a Grand Finale where the Nephalem stands against both the High Heavens and a Resurrected Prime Triumvirate. Before the second expansion is released, content patches could patch in some of the Adventure Mode areas, events and bosses into campaign as a "prelude" to the second expansion.

Diablo is doomed at the second expansion

Diablo has always been quite a planner. Do you actually find it weird that for once, he did not pull a You Have Outlived Your Usefulness on Adria once she succeeded jamming the Black Soulstone to Leah, reviving him? Instead, he sent her away until her services are needed. What does this imply? It means, Diablo has planned things since the Wrath video, and Adria would have been part of it, in case he's back for some reason.

Too bad the Nephalems had to ruin it by killing Adria.

Unless Diablo already have a backup plan in the absence of Adria, I think his defeat would stem from the realization that the Nephalems ruined his plans even before Malthael released him.

Adria was the reason why back in Diablo II, the Sorcerer became the Summoner

What was known from the Sorcerer/Summoner became crazed was apparently because 'he fought too many demons'. However, if you recall and play the first Diablo as the Sorcerer, you will visit Adria a lot. And knowing that Adria eventually became Diablo's servant quickly after Aidan's trip to the underground of Tristram, who is to say that as a Kick the Dog moment, she influenced the Sorcerer with either magic or rumors that his path to insanity became a straight road. Considering Adria's true personality, this might make sense.

Imperius and Tyrael will reconcile

A future expansion will cover the remaining Sin Lords

So far, we've seen Lords of Gluttony and Lust in the base game, and the Lord of Envy in the 2.6.0 update for those with Adventure Mode purchased. If the game is going to use expansions to introduce new Sin Lords, it should only be logical that a future expansion or two will cover the remaining four, possibly even adding a new Act revolving around the remaining four Lords plotting something together.

The Eternal Conflict is part of the Xel'naga's Infinite Cycle.

The angels have purity of form similar to that of the Protoss, and the demons have purity of essence similar to that of the Zerg. Which would make their offspring, the Nephalem, akin to the Hybrid.