Assuming that the Let's Go Pikachu/Eevee "rumor" is real, why would Game Freak make a game that only had gen 1 Pokemon in it, including the post-game? Wouldn't that piss off a lot of people because not everyone's favorites were from gen 1 you know. That would be a PR disaster and fans would feel betrayed knowing that their non-gen 1 favorites have been scrapped.