You'll take your Dokihadronchlodur Galar Gmax Megadon Green Foliage and you'll like it.

Could make millions off nostalgia alone.

Or not. I doubt they have any planning materials or source code (assuming the whole thing wasn't written in assembler from the get-go) left for the early games, so they'd have to reconstruct everything. They wouldn't use information collected by fans to help, because businesses just don't. The end result would likely be less efficient, and therefore less profitable, than starting a new Pokemon game from scratch.