It's my understanding that the flying mounts will only be useable in the Floating Continents area. This will only be a fraction of the game. They've talked about this long ago in the past, how they didn't want to add flying mounts to the whole game because it would take away from the world. So I think they're going about it the right way. The difference between WoW and FFXIV flying mounts is that SE is creating the content specifically FOR flying mounts. Blizzard just kept adding the same type of zones - never understood why they didn't really utilize the ability to fly upwards.