I've been studying the First Nations of BC in college this year, and would absolutely love a region based on it. It would be really cool if each city corresponded to one specific indigenous group and represented them. Like, the electric gym could be in the city in Kwakwaka'wakw territory (the thunderbird is pretty prominent with them), the grass gym could be on Haida Gwaii (Haida are well known for their wood carving), the ground gym could be in Secwépemc territory (that area is famous for its pithouses) etc. And there could be plenty of cool pokémon designs based on their lore and similar things. Maybe there could be legendaries based on the trickster characters (raven, mink, coyote, jay, etc.), and there could probably be a whale pokémon for the southern Vancouver Island area (whaling is a big cultural feature of the Nuu chah nulth), and possibly also a pokémon that could use Bone Club to represent the actual use of whale bone clubs. I'd also love to see a Copper pokémon (maybe a new steel type?) and it would be neat for there to be a salmon pokémon that evolved into a sisiutl-type serpent to be magikarp's successor (salmon were supposed to turn into these double-headed serpents much like carp became dragons in Eastern Asia). Also, considering that area has well known legends where salmon can be eaten and have their bones turn into people unharmed, it'd be cool to give the salmon pokémon 2 forms, one like a fish, and one like a human, maybe its ability gives it a second HP bar, and it would turn into a human with full HP again instead of fainting, but any hits done to its fish form would heal the attacker by the same amount of damage done to it? Might be cool to incorporate that legend somehow. Also, a fire/water eulachon pokémon would be really neat too!
I'm honestly really crossing my fingers Alaska won't be the next region, because that would not only be a 3rd region based on somewhere in the United States (so far, the games have only taken place in 3 countries, I'd really prefer more diversity than that), but it also would probably be too close to BC to allow for it to ever become a region of its own.
Guyana's second on my hopes list, especially considering it's got precedent already in the pokémon world (it's mew's native homeland, apparently). Kaieteur Falls would make a great attraction, and it would be cool to have a local common bird which was a kiskedee that evolved into a cattle egret. To think of it, the continents of the southern hemisphere have been pretty largely ignored so far. Except for Oceania, which was represented by the second region based on one of the United States :/ Really, it would be great to add South America and Africa to the Pokémon world somehow. In the latter's case, probably Subsaharan would be better; as much as I love Egypt, it's already got its fair share of references in pokémon, while the rest of the continent is pretty conspicuously absent in terms of representation.