Well, given the fact that there is still one citystate in Eorzea still inaccessible at this time (Ala Mhigo), it's hence highly likely that will be where the next expansion will involve. I could speculate on how the story will turn out to provide the reasons for heading east to Ala Mhigo, but I won't as I'm usually way off the mark, although at the very least freeing it from Garlean control would probably play a major part of that. Once Eorzea itself is fully explored and accessible, I think that will be then when SE decides to expand the world and take us away from Eorzea to other continents like Othard.

And given that Ala Mhigo is my character's birthplace (according to her backstory that I wrote), I'm even more eager to finally see the former kingdom where Enki was born and spent the first years of her life.