Through ARR, there were lots of references to Ala Mihgo, and a lot of interactions with various refugees. We went there in Stormblood.
During ARR, we were introduced to the Doman refugees, and Doma was usually referenced pretty much any time we interacted with them. In Stormblood we went to Doma.
During ARR, Ishgard was mentioned often. In Heavensward, we went to Ishgard.
Of what we've seen mentioned so far, and what we know of the world, going deeper into Garlemald seems like a good possibility. But beyond that what other possibilities do we have?
Further discovery of Sharlayan? Is there anything else we've had mentioned to us that I'm not thinking of that could potentially be a destination in the next expansion?