I had an idea on how to make flying a little less appealing (or a lot more) appealing on PvP servers.
Make flying mounts have an HP pool and attackable in air. When the mount gets to a certain HP level the character is then dismounted and free for you to fight in face to face combat, if they survived the fall damage.
I believe this will make flying more fun for max level characters and less appealing to low level characters. Since while on a ground mount they can continue to run from an attacker without fear of being dismounted, so it will become the safer form of travel.
This attack ability could be applied to all flying mounts, but I personally believe it should only be added to new mounts earned through PvP. This would help ensure that flying remains more appealing to max level characters and less appealing to low level characters since they cannot fight back.
This will help force low level characters to the ground and potentially reignite a new for of world PvP.