Lets say next games are Pokemon Star and Pokemon Z. Both are third versions and sequels of SM and XY.

Star has Alola only, new form of Necrozma, 20 new Alola forms, new forms for starters, Pokemon World Tournament in the place of Royal

Z has Kalos only, permanent Perfect Zygarde, 20 new Mega Pokemon, Battle Bond forms for Kalos starters, Battle Frontier next to Kiloude city

Kalos has now Ride Pokemon: Lapras (Surf), Charizard (Fly), Sharpedo (Waterfall and smashing rocks), Gogoat (Rock Smash), Mamoswine (Strength), Furfrou (Itemfinder), Rhyhron (riding on rocky terrains)

Alola now has gyms (Mina, llima, Lana, Kiawe, Mallow, Guzma, Plumeria, Molayne)

Both regions deal with the same evil team consistingof bitter ex-members of Teams Flare, Skull and Aether Foundation. Malva is the leader in Kalos branch, Faba is the leader of Alola branch. There's one island (south of Kalos, north of Alola) thats in both games and thats where plot of both leads to a climax

Kalos has Lillie visiting and battle , Alola has AZ visiting and battle. If you link both games you can get Lillie battle in Alola and AZ battle in Kalos

Would you buy a game like that? Both?