We have a conclusion! The secret church in Nier: Automata that’s been puzzling players all week has been confirmed to be a mod.
Earlier today, reddit user sadfutago – behind all the videos so far – posted a link to a Twitch stream that revealed all behind the previously unseen secret church area and its use of Nier: Replicant assets.
The stream showed various assets from the game and the secret church area, before admitting all was done through an in-game mod, which will be made available publicly. The VOD wasn’t saved but you can still watch clips of the broadcast.