There are a few areas everywhere that could be made into zone lines. I had a list of them at some point, wonder if they'll be used in Heavensward or if they'll end up like the countless dead end caves XI ended up having...
Still, given its location I can see the gate in Central Thanalan right next to Ul'dah and the zone to Southern Flanalan being used. I was expecting the Gold Saucer to be floating based on the screenshots, so I expected Revenant's Toll to be expanding into an airship dock to take us there (again why I expected Rowena to be involved), but since they went for a "true" Gold Saucer by sticking it in the desert I'm not sure. Probably shouldn't be able to walk to it if it's anything like VII...