The new Pikachu and Eevee games will only feature the original 151 Pokemon:
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You can't transfer Gen 2 or 3 Pokemon to it.
Also, in my opinion (not like it matters much), these games look absolutely terrible. Like, I thought they were going to be bad, but Game Freak really outdid themselves. No more wild battles? Every wild battle now replaced with Pokemon Go minigames? Every Pokemon battle can just be a 2v1 now, so all challenge is removed from the original games? More Kanto **** sucking? Oh man. How the mighty fall.
Glad we'll be getting an actual core game in 2019 though. But they'll probably screw that one up as well.