Frankly I hope they just add flying as they always did in previous expansions rather than these account wide achievement grinds in future.
Its prooven to the people that like flying (which is evidently NOT a minority given how many people have hype for 7.2 purely BECAUSE they can fly in Legion) that Flying is a pivotal part of wow's lifestyle.
People bitch that no flying is more immersive and better but frankly the game had flying and sky cities and space cities long before they tried cutting it back. Honestly, all it does is hold back the game.
Blizzard has failed to capitalise on flying as a form of immersion, gating certain end game content behind requiring you to fly, instead of having no flying at all.
Maybe in future we can have some mountainous regions too high for any boost to reach, requiring you to fly to get to them, and equally have areas where you can *only* fly to a certain point before being forcefully grounded like an Aa tower shooting you out of the sky.
Or, maybe theres flying islands that literally are where the raids/end game zone is requiring you to fly to reach it.
Frankly, it would be better for the game if it had flying, because it would be relevent again if they actually focused on making it immersive.