Think of it like this, since flying will inevitably make its way back into the game via an achievement we have to complete, why not make a complete zone that has content dedicated to players who have the achievement and can fly?
For example, once you get the achievement and can fly, a new zone opens up that has several floating islands with waterfalls, and nether fragments and such that you can only access if you fly to them. It can be a complete questing zone with tons of story and flight based quests, maybe even quests that pit your flight skills against mid air obstacles etc.
Imagine outland nagrand with no ground, but on a much grander scale, and more varied; only islands with all the quest content on them.
There could be caves in the floating islands, dungeons, maybe even a raid.
Would you like this type of content? (since we have to embrace flying anyway....)