Frankly I am relieved.
I'm looking forward to getting each and every one of the class mounts (maybe apart from certain colour variants) and when I read you needed to be exalted, that made me sad. Mostly because having to go through those lengths on 12 different characters is aggravating, none of my characters besides my main are exalted with hardly anything.
I'm also happy it just requires the Armies of Legionfall achievement because that's just a series of weeklies that when you've done one the next one unlocks automatically as long as it's already unlocked via gating.
My original plan when I heard of class mounts was 'Yay I'm gonna get all these! Starting with my least fav and finishing on my fav!' , then I heard it would take 11 weeks and I got sad again, BUT then I heard that's just gated, not it TAKES 11 weeks to get :P
If anyone complains you should get to exalted before getting them, then get to exalted before you allow yourself to proceed. Otherwise, noooooooope from me!