Sounds about right. ^_^
For an analogy (why didn't I think of this sooner? o.O lol), let's use Google's search pages. They have their main search page, which is in English/US, but then they also have search pages for just about every other country/region on the planet, right?
I'm in Miami, so, by default, I'd prefer to use Google's main search page due to relevance and whatnot, but there's nothing preventing me from also using Google's other search pages, like for the UK, Canada, or any other country (except maybe a language barrier), just as there's nothing preventing a Brit from using Google's US page.
Same concept with Square setting up servers in new regions, yet still keeping them all open to all players.
I don't see why wouldn't be able to play together, btw, what with being able to create at least one character on each server in ARR. I'll probably be re-rolling on a US East server, if they go the route of setting up East/West coast shards.