Yeah, but that aspect might not. Trading Pokémon from 3DS to Switch shouldn’t be a problem at all since the 3DS and Switch versions of Monster Hunter XX are able to connect. If not that, there’s also the Pokémon Box cloud storage thing.
I can’t see this game not including post-Kanto Pokémon. I mean, it’s rumored to be a kind of sequel rather than a remake so why no newer Pokémon?