I believe Yoshi said there would be special airship-only zones. Like "Above Thanalan" which would encompass North/South/East/West/Central Thanalan and you could see the landmarks below like UD and the Castrums. Like you said, the current zones are WAY to small for airships to fly above players. I think Yoshi also said something about when you're on the ground, you can look up and see AI airships flying around giving you a sense of how many player ships are in the "Above ____" map.