Mountacular

Blizzard announced that in WoD, you'll be able to see all mounts on all characters in the new mount interface, including faction specific mounts (though you won't be able to use opposing faction specific mounts).

My question is: do all mounts now count toward this achievement with this change?

The reward for this is the previously data-mined item that was never available in-game: [item=69226]
A little behind (by about 3 years) but glad we finally got our Green Fire Hawk!

today, I was talking with GM about problem with not counting few mounts toward this achievement. After he resolved my problem I asked him about profession and personal achieved / class mounts, to be 100% sure. He confirmed my what you guys already post here.

This achievement can be earned, only when you have 250 usable mounts on current character

which means gladiator mounts, mounts from challenges earned by different character DOES NOT count toward achievement progress in current character. Also profession mounts which required skill with that profession and current character don't met requirements, those mounts also DO NOT count.
Also confirmed:

4 mounts from Ahn'Qiraj counts to this achievement

so If you are missing few mounts to earn this achievement, previous one or 300 mounts achievement. And If you have plenty profession mounts, I recommended you create new paladin character, level him to 80+, get [item=47179] (you can get it in less then one month), skill up Tailoring to 300, Engineering to skill 375, and your "mount achieve" character is ready.
+ 3 class mounts [item=47179] , Summon Warhorse, Summon Charger
+ 4 Tailoring only mounts Flying Carpet, [item=44558], [item=54797], [item=115363]
+ 2 Engineering only mounts Flying Machine, Turbo-Charged Flying Machine
So, if in the future you will miss few mounts, you can log to this paladin and can get opposite of for example priest without those professions even + 9 mounts.

hope this post help some of you fellow mount collectors, +1 if tyou like it, thank you

English is not my mother tongue, sorry for bad grammar