Have you seen any flying mounts in the battlegrounds? No? NO!? What is the reason i wonder... ?
Let me explain my point of wiev,
PvP cant happen in the air, thats why there is no world PvP, world PvP usually happened when someone ganked someone on the ground then the victim calls his guildies and the ganker also calls for help and here we go a massive fun melee. Or when a huge horde/alliance army invaded sentinel hill/crossroads looking for trouble, this thing ended when flying mounts were included in azeroth. Well, PvP CAN happen in the air, but only if you are a druid with a parashute. Now when somebody sees somebody that could kill him-pooof-in the air making a rain of urine....
Have u seen the beach at Twilight highlands or the zones in Hellfire Peninsula? Some flyers just circle eachother and wait for the other to shoo off, then they land, cap and run with their tail between their legs. I say they should fight to see who is worthy of capturing the point. It isnt king of the hill if both armies fly around the hill waiting for eachother to leave out of boredom.
Flying mounts are so much fail, nevermind they are really usefull for and stuff, THEY ruined the world PvP, not the players.
They also ruined the feel of exploring new zones while on the ground by having an option to just fly over them and see all the scenery (but its being adressed...kinda)