Easy fix. Just put in a quest similar to pathfinder. Complete that and allow flying. Difference being, put the whole damn quest in so if people want to actually complete it. They can. If you want to take your time, you can do that too. Up to the player.
Be upfront about it right from the start. Design that quest to be entirely in at content/area launch. No BS of you can complete it later at some random time/patch.
Sure, you will still get a few that complain but nothing like the vague, mid expansion BS or the crap that happened with WoD.