Reminds me a little of the Ultima V - Lazarus[1] project, where volunteers re-implemented the entire game in the Dungeon Siege 3D engine. They also added tons of new characters and dialog, side quests, a richer plot, and new artwork and music. They did all this and managed to keep the major plot and game elements the same. They actually managed to greatly improve on what is unarguably :) the best Ultima of the series.
How do they handle hidden dialogue options? One of the most amazing things about the series before 3d was you just talked to people about things and often they had something to say about the topic. Like you can ask just about anyone about the avatar or blackthorn. There’s a donkey that figures out he’s inside a video game, etc.
1: https://www.u5lazarus.com