The only Pokémon I thought of in terms of being meta relevant were Eggy and Golem. Eggy would be interesting if it learned Dragon Tail/Outrage combo or Golem with some weird combo or electric and steel moves. Maybe charge beam/thunderbolt as some weird tanky electric type but he would be horrible against Pokémon with ground moves. I do like the idea of Alolan Sandslash, really liked him at least
Alolan forms! My favorite coconut tree is coming!
https://pokemongolive.com/post/alolakanto-pokemon
Answers
I don't know how Niantic will go about this, because in the games you had to be in Alola for some to evolve (for ex, you took your eggs to Alola from any other region, they grew into longneck coconut tree).
I guess Niantic will either create special Alolan items to use on them, or you have to catch them in the wild and are predetermined Alolan ones. Or maybe a mix, Alolan items for those whose prior forms are like Kanto ones (pikachu, exeggcute, cubone) and Alolan wild forms for those who are completely different (geodude, meowth, grimer, vulpix, rattata, sandshrew, diglet). Or maybe just quest rewards.
Yeah for example: "In Alola, Raichu has a regional variant that is Electric/Psychic. It evolves from Pikachu when exposed to a Thunder Stone. All Pikachu in Alola will evolve into this form regardless of their origin." ~Bulbapedia.
But if we were to go by that, in GO we'd have to take them to Hawaii. But I hope it's just a different evolution branch for them and the other ones they share common pre-evolutions.