No Flying in Classic, mounts at lvls 40 and 60 (walking for the first 39 levels)
Flying in Burning Crusade originally was not available til 70 (start questing at 58)
Flying in Wrath not available til 77, required additional training (start questing at 68)
Flying in Cata, available instantly throughout Azeroth as this was a remodel of the planet and the zones were vastly spread apart
Flying in Mop, available at 90 (start questing at 85)
As you can see, Cata broke the pattern and spoiled everyone, and now Blizz is seeing just how big a mistake Cata was. Things that should have happened: No tabard rep grinding, no easy heroic gear, and flight in Cata zones til 85 (not 80). Even Vash'Jir was a no fly zone since it was under water.
Like with EVERYTHING in this game, it was eventually nerfed, lowered, or handed some type of option around the .2 or .3 version of the expansion. Since 5.2 is being tested now, I would say if there is a flight restriction lifted or reduced for MoP, it won't be until at least 5.3. Folks need to just hold their water