On May 21st Niantic announced that one of the latest features that will be added to the game is Alolan Forms, a feature only available in the latest console games. No other information has been given about how they will be implemented or what it means for the other Pokemon of Gen 7.
Here is a list of all Kanto Pokemon which have Alolan Forms. The full announcement text is below.
Identical stat Pokemon
Sunny days are ahead! Whether your forecast calls for rain or shine, we’re celebrating all around the world by introducing some special Pokémon from the tropical Alola region to Pokémon GO. Get ready for some of the Pokémon originally discovered in the Kanto region to appear in their Alolan forms! These unique variants were first seen in the Pokémon Sun and Pokémon Moon video games, and they will make their way to Pokémon GO in the coming weeks. Keep an eye out for news related to this exciting change—and don’t forget to tell your friends! Stay safe, and happy exploring!
—The Pokémon GO team