WMG / Bravely Default II

Seth is from Luxendarc and is Tiz and Agnes' son

Seth is stated to be an amnesiac who washed up on the shores with no idea of how he got there. He is a Gender Flip of Agnes both in personality and appearance while having the stats, voice, and mannerisms of Tiz. And, in a game where everyone is clearly English, Scottish, or Irish, he is the only character to have a very distinct American accent.

It is plausible that perhaps, the Holy Pillar has been activated again, and Seth - when called to investigate the same by his parents, ended up estranged in Excillant. His conflict will be about getting his memory back and being made to choose between the world of his birth and the world where his new friends reside.

Building on the above, we will see the other children of the original heroes of BD and BDS

Assuming Seth is the son of Agnes and Tiz, it is likely that he was friends with Yew and Magnolia's and Edea and Ringabel's/Alternis' children, and even had them as part of his original party before he was whisked away to Excillant. They will probably make an appearance late in the game, and with them will come The Reveal of Seth's true origins.

• Jossed. Word of God has said multiple times that Bravely Default II is completely separate from the other games, and Seth ultimately has no connections to any previous characters in the series.

Elvis is totally gonna betray the party/die in a heroic sacrifice.

He is depicted in the Black Mage's asterisk gear in official material, indicating that he is the actual owner of the Black Mage Asterisk, because of this, he will eventually betray the party, perhaps in an effort to steal the rest of the Asterisks, Adelle will have become too loyal to Seth and Gloria to go with him.
Alternatively, he'll instead die in a heroic sacrifice.
As the first game was a spiritual successor to Final Fantasy V, it will be handled similarly to Galuf's death, and we'll get a new younger character who inherits his abilities.

• Jossed. It's Gloria who has to perform a heroic sacrifice to seal up the Night's Nexus. In another bad ending, Adelle chooses to stay behind to help keep the Night's Nexus separated forever from the human world. The true ending has them permanently defeat the Night's Nexus so they can all go home.

The Planeswardens will play a role in the story.

Bravely Second established that an organization of interdimensional guardians exist and that Ringabel has joined them, Excillant is just one of those worlds they protect.

We may even encounter Ringabel himself.

• Jossed.

Combining the above two, Ringabel himself will replace Elvis.

That's why they're so similar. He'll inevitably flirt with Adelle, but will make it known his heart is with another.

• Again, jossed.

The "II" in Bravely Default II is not a roman numeral.

Rather it's the subtitle of the game that carries a hidden meaning that will be revealed in full after a Wham Episode, just like the first two games.

• Best guess for now? The "II" forms the letters d and b to become "holdback".
• Word of God has already stated that they won't do anything like that again on account of it being too obvious by this point.
• We'll see if it becomes a case of Trolling Creator or Lying Creator.
• Ultimately jossed—no changes are made to the title later in the game.

There will be DLC that'll introduce new Asterisks to the game.

In Default II, there's a total of 24 Asterisks (25 if the unobtainable Librarian is counted). A majority of the Asterisks (those you obtain through battle) have mysterious symbols on them. These symbols actually represent letters of the alphabet, as shown here.

Since only 22 of the Asterisks are obtained through battle, we only get to see 22 of the Asterisk letters. And it's safe to assume that the Black Mage and Librarian have symbols as well, bringing the count up to 24. With DLC, it's a good way to complete the Asterisk alphabet by bringing in two more jobs to bring out the missing letters. Additionally, each of the numerical symbols from 0-9 have symbols as detailed above as well.

So, if DLC is added, we could see twelve new Asterisks in play—two for the remaining letters of the alphabet, and ten more for each of the numbers.

• not practical, punctuation would also have to be added, meaning at least 17 beyond the alphabet and numerals, resulting in jobs with no Identity at all

The Black Mage and Pictomancer used enchanted material from a wald ash tree to make themselves appear younger

Lady Emma looks so young because she uses material from a wald ash tree that's been imbued with a spell to enhance its power, as it can also function as a Fountain of Youth. It's confirmed that a wald ash branch, if imbued with the spell Roddy and Elvis cast on it, can be used to kill the undead by restoring them to life and causing them to die of their mortal wounds for good. It's also confirmed that the wald ash tree is "full of life". In addition, Folie looks like a child because she also uses wald ash material, and this was how she had a branch of it to help make the creepy doll of Mona she gave to Lily to take care of in the forest.

If there's DLC, it will focus on the Asterisk Holders that survived to the end of the game

This stems from a fake DLC announcement made for April Fools' Day from the game's official Twitter account. While the announcement was, of course, fake, it does open the window for future DLC featuring the Asterisk Holders that haven't been killed.

Particularly, there could be five DLC packs: one focusing on the surviving Halcyonia Asterisk Holders, one for Savalon, one for Wiswald, one for Rimedhal, and one for Holograd.

If theres DLC it will reintroduce the Bravely Second Mechanic.

And possibly set up a direct sequel to 2.

If there's DLC, it will include the Prisoner Asterisk that was featured in the game's April Fool's DLC announcement

A Prisoner Asterisk could be a rather interesting Asterisk if it was actually created, so perhaps a potential DLC pack will allow players to use it.