I think this is actually a very perceptive point! Nintendo loves to throw in super obscure little hints like that into directs and trailers.This might be a little bit of a stretch, but to support the location of it being based off of Hawaii before the development montage, when they were trading Pokemon a Ocean pattern Vivillon was traded. They are only found in the regions of Hawaii and off an island of Madagascar.
The more discussion that's happening in this thread, the more I think that a region of island hopping around Polynesia is likely, and the more excited I get about it. Water-Type is the most diverse type IMO (though there are more of Normal-Type Pokémon) and it might mean that oceanic encounters are actually a little more diverse for once, like birds or random other Pokémon knowing Surf (like Rhydon or something :L). It's also actually somewhat of a risk, and I think that if it is a region around Polynesia, it could actually be the best games in the series yet.
So long as they give you a normal Exp. Share in addition to the Exp. All and difficulty settings, because the games are way too easy rn and making the trainers a little bit tougher would be a really quick and simple job.