Well, people write what they know. And most (if not all) of the writing team is Canadian or American (honestly they could all be Canadian, not sure). When the team tries to go outside their comfort box they end up leaning towards stereotype and cliche (see: Kasumi and Kai Leng). So... not sure I would encourage them to do that.
You can write about something you don't know with some understanding and research, but it would be more likely to work with the story set on earth. Would it be interesting in this case?
I wouldn't favour strong accents either, it possibly just pinpoints the character being a bit foreign in that setting, especially with aliens around being heard speaking english. (Slight accent can be charming, and unavoidable, and people just have different habits to speak anyway, there doesn't need to be a story behind it every time. Though english ain't my 1st language so english accents are mostly something lost on me...) People living in space colonies and Citadel have likely developed their own slang instead of reminding of specific earthly countries too closely.
I'd like to see more variance among npcs, since they're not all going to look like same anyway. I'd love to hear more countries mentioned because some of us are left out so often - that's just not something I'd like the writers to concentrate on very long and hard, when there are other curious matters and species (and personalities) you wouldn't find in other/most games to think about. If anything, I'd like canadians to be represented a lot. I don't know much of the country though, it seems relatable enough, and it's always nice when author can provide authentic viewpoint. USA is a cool country of course, but others should serve as the "default" sometimes too. (I don't really care for nationalism, but I don't mind each series having some quirks.)