Aight, we all know that theres an invisible roof, over all zones... which prevents you from flying further up into the air.
Well...
When you get to uldum, and fly to the tower of "Throne of the four winds".
Once here, you fly to the very top of it, and you'll notice that you hit the roof, now this roof is on the exact same height as the very top of the "Throne of the four winds"'s top tower point. - So, once up there, dismount and force yourself to the top, now u can get on ur flyer and wupti, infinite height.
Step 1)
Get a flying mount
Step 2)
Fly to Uldum
Step 3)
Fly to the tower of "Throne of the Four winds"
Step 4)
press your spacebar and fly as high up as possible
Step 5)
Aim your character to the top of the tower.
Step 6)
Dismount as soon as you notice youre stuck between the tower and the invisible wall.
Step 7)
Mount up and fly.
Step
Do whatever u want