I think insta teleports remove immersion and shrink the world, and also destroy game design. Players just zip anywhere they want lazily and skip content.
Queuing for lfg and lfr is also skipping content, teleport to instance, no challenge or gameplay. People should have to run to the instance entrance and click a stone to lfr or lfg, no summoning stones.
Hearthstone cd should be increased, because this is an mmo, and a rpg, and both, and people should have to traverse the world.
Flight paths should enforce a cooldown of 2 hours between each one, and they should cost 5 times as much.
When I RP in Pathfinder it takes days to travel anywhere, and lots of random shit happens along the way. WoW should be like that at max level.
If flight can be blamed for skipping content, so can all those other things. Turn them all off to see how it goes. Why not lol.
Seriously though, I do like the mounted combat available in the game atm, and I could see it easily being implemented into a flight zone with mounted aerial combat.