If it were up to me, you wouldn't be able to transfer ANY pokémon whatsoever from old games.
Fuck all those old hacked genned shitmons people have. Kill them all. Let the Switch and onwards have a fresh start without decades worth of hacked junk. Obviously let people catch old pokémon in the new games and eventually get them all back, but break all pokebank/pokemon home connectivity. Fuck old trash, fuck hackers and fuck genners.

Tabula rasa.