At one point, Legacy was going to be an AU of Universe A. It was then changed to a Soft Reboot, before eventually morphing into a true sequel.
In the planning stages, Arkn: Legacy was codenamed Arkn X. The name still applies; however, Legacy is the official name.
Originally, the Paradox Players were supposed to carry over to Universe X in some form. DeathlyLogic and co. tossed around the idea of having the "core four" survive the final battle and become the Hethe of Universe X.
Another idea was that some of the Risen and main protagonists would be reincarnations of the Paradox Players. (Ryael as the reborn Raziel, Faust as the reborn Raphael, the former character Malachi as the reborn Michaelis, and a character named "Vulture" as a reborn Uriel.) This is why there are strong similarities between some of the characters and the protagonists of the Arknthology.
Malek was supposed to survive into Universe X. He would have been a wanderer and hermit in Destrus, with only the tiniest fraction of his old powers of creation (enough to summon water and the occasional Pizza Rolls).
Originally, the only humans eligible to become Elekti were those who had not only impressed the Hethe during their earthly existence, but shaped the course of human history. It was decided that this was too restricting, and it was revised to Cedric choosing the Elekti at random because he finds them interesting (with the interpretation of interesting being left up to the individual writers, allowing for a bit more leeway).
Initially, both Deebo and The Carver were both going to appear in Legacy, with their Universe A roles swapped: The Carver would have become a true Hethe (i.e. distant and seldom-seen); Deebo (whose power was greatly diminished) would have become a mysterious, skeletal being who went by the name of "Baron Von Squeezy" (or "Joe") and had both horns and wings — the latter of which would have grown out of the blood of those he had killed (causing him to trail blood wherever he went).
Type0Negative was set to be involved in Legacy. Among his planned contributions were:
A blog called Tales of the Destrus, introducing a character called Vulture who would be the Legacy equivalent — or reincarnation — of Uriel (see above). Unlike T0N's other concepts, TotD was actually created; a single entry was posted before the blog was cancelled and deleted.
A vlog featuring a new incarnation of Alex Winter, a young man by the name of Oliver Crow who is a patient of a reborn Dr. Ellis (Dr. Ellis Matthews). Type0Negative made a post teasing the series.
Staff of the Scholar
The Reign Experiment, a series conceived by Penthepoet. It would have been the first true Arkn Mythos horror series (aside from Handprints), revolving around a human (who answered to the name of Scholar, and was a prototype Faust) who is forcibly turned into a Dekn via Lumeric's drugs and must struggle to adapt to their new life. Said human would have taken the name Paimon, eventually evolving into a fucking Nartholese-speaking badass.
Fausts character was originally going to take control of the Arkn Yakuza/Miran'khai. Penthepoet eventually decided it was a bad idea and scrapped it. Season 2 of Staff of the Scholar would have revolved around the now Miran'khai leader Faust chasing down the Arkn X version of the Hooks Killer.
One scrapped character for the series was Petrel: an Arkn boy whom Faust would have befriended and had a really solid dynamic with, until it was revealed that he was a spy for the Arkn Yakuza and was supposed to bring about Faust's forced initiation into the group. He still appears in Legacy, but in a different role than originally planned (while the dynamic that would have been between Petrel and Faust appears to have been transferred to 4boy/For'ende and Faust).
There were also plans for Petrel to appeared in a vlog episode of Staff of the Scholar, even after his "Arkn Yakuza" role was scrapped. However, the actor was not available to film for the role.
There were also ideas for another, similar character named Aberdeen, a Yakuza hitman who would have approached Faust and tried to "train" them to become the leader the Yakuza needed. (Penthepoet has stated that he may still appear in Arkn: Legacy in some form. However, if he does make an appearance, his role will be greatly reduced from what was originally planned.)
The Claw of Barbatos (the artifact that Faust got from the Lathyrum) was planned to have a bigger role in the series. It would have appeared on camera and been used by Faust. However, Penthepoet couldn't get the prop for it and instead picked another route.
For'ende Elext was originally going to be a stale, one-note character used to take over Faust's blog and keep it active while Faust was gone. When Petrel's actor flaked out, Penthepoet decided to expand For'ende's role to that of a solid secondary protagonist.