Update 6 is going to add a "Truer Ending" where we must defeat the Leviathan before it can wholly resurrect
The Assignment Anya update seems to be really playing up the Mors Mundi cult as the Greater-Scope Villain of the game even moreso than Diavola, and the Milkbar Lads have repeatedly said that Update 6 will be the biggest and most content-filled update yet. Thus, it's easy to infer that Diavola will be downgraded to just a Route Boss and some form of the Leviathan will become the game's True Final Boss in one final confrontation for the fate of the Estate.Lambert is going to be revealed to be part of the Mors Mundi cult
In several of Cordelia's logs concerning Lambert, she says how bad it would be if he unexpectedly returned home what with the current predicament. But what if he's already there, working with Cybil to help resurrect the Leviathan? Not only would this be a huge twist, but it would be a great way to contrast him with the rest of Cordelia's family as their Token Evil Teammate.