Flying as it exists in WoW needs to be changed, the version we have is so stupidly broken as a movement option that the only possible way ot balance content around it is to completely remove it.
Alternative movement options completely fail when compared to the option that is mounting up and flying from anywhere.
The current compromise offered players is that flying is disabled entirely until later in an expansion, which does work in giving flying, but doesnt really satisfy either camp. Those who want the convenience of flying only getting it when the content is mostly deprecated, whereas those that doon't want flying to instead focus on better open world content essentially having their preferred version fo the game removed halfway through.
What I then propose is a rework of flying that instead nerfs it in such a way that most of the convenience, in this case quick movement is preserved, with ground content still being a regular part of the game.
Quite simply, flying is now only allowed from set points in a zone.
To help visualize how thios would work imagine the zone of Maldraxxus. In this system flying could for example only be possible starting from the Seat of the Primus, you could then use flying to reach wherever you wanted on the map unhindered, though when you land and engage in content on the ground you would be locked to the ground, necessitating the use of ground mounts, with all the pros and cons that comes with it.
In this way flying could be introduced earlier as the essential factor of ground content being a part of the game is preserved.
Secondly it would also make the rules of flight more transparent. Absolute no-fly zones like Throne of Thunder or Argus would not be ground mounts only because flying is disabled, but instead because there does not exist areas that allow you to start flying.
Another great factor to this version would be that flying could more easily be made easier or harder simply by adding more areas that allow flying in a zone. If Blizzard wants to use, say, the Barrens as a questing zone, they do not need to dismount players who fly, or similar tricks, but instead simply remove the areas in the Barrens that would allow you to start flying, allowing a far more organic and seamless exploration of the world that both allows flying and also doesnt completely undermine the idea of the game being ground based.
Further discussion on alternatives to the current flight system as a whole welcome.