I'm guessing, given they're relying on private financing, the ability to reuse assets from TP1 is the major reason to make it a sequel instead of a new IP.

Personally I liked TP1 a lot for the most part, but I agree that the ending was a horrible misstep. I'm not adverse to metafiction, and this is Gilbert after all, that's kind of his jam, but the sheer nihilism of it all left a horrible taste in the mouth. Ironically, for someone who cares so deeply about game design, it felt like an ending entirely borne of Gilbert and his fellow designers pleasing themselves, instead of thinking about how it would feel for the player.

That said, I'm still glad there's going to be a sequel. Hopefully it has more of what I liked and less of what I didn't.