What could Blizzard do to make flying feel integrated into WoW?

I’m really glad that flying is now available in Zereth Mortis, but I’m also confused as to why it had to be unlocked in the first place. And that connects to a general feeling of flying being a problem — that zones are designed without flying and thus flying has to be locked off until certain milestones and achievements unlock it. We’ve seen this process over and over again, from Mists of Pandaria making you buy a new rank of flying to Warlords of Draenor restricting it until the final patch, and Legion introducing the Flight Master’s Whistle so players could get an airlift out once a quest was finished, but had to make their way in on foot so that all of the monsters and threats of the zone had to be traversed.

I’m not even saying that’s a bad design choice, but it does make me think that flying is an afterthought at best, and an actual detriment to zone design at worst, which feels weird for a feature that was literally touted as a major add to the gameplay of The Burning Crusade, and one that saw the entirety of old world Azeroth reconfigured to accommodate it in Cataclysm. Why does flying seem so disruptive? Considering how much of the store is unique mounts, it feels weird that half the time we can’t even fly on them.

And what could be done to make flying feel more like a part of the game, more integrated into questing and zone design, instead of an afterthought or a nuisance? Cataclysm had flying in every zone and frankly I never felt like it trivialized anything — there were still hazards to fight, quests to clear out, and my ability to fly around meant that the whole space could be utilized. Is it as simple as going back to that approach? Or would there need to be more of a design change for it to work? How would you implement flying as a part of the whole experience in World of Warcraft?