Imagine a Master Collection with a game per region that can share one OT:
>Start
>New game
>Would you link this game to another?
>Yes
>You start with the ID number, gender and name of that linked game
>Pokemon transfered between linked games maintain their friendship and affection levels

FRLG, Platinum, HGSS, B2W2, XY, ORAS, USUM, SwSh games (single game per region), each one with all 898 species and forms included, you can put and take any pokemon through PokemonBank

All legendaries, mythicals and UBs are available, with their own location and event in their respective regions.