First of all:
Wonderful Idea.
What I'm really hoping to see from this is a mix of horde only, alliance only, class specific, and then generic forms of these cosmetics. I hope we don't just get one line of cosmetics per faction / class and they call it a day.
Would be interesting to have ones like a backpack, or just a normal satchel that you could choose to put on your character, or you could go the faction route and make it look faction specific. I'm really thinking flexibility here is the key.
Out of all the news I've heard for WOD, I think this is getting me the most excited because there are so many routes they can go with this. Adding these rare cosmetic drops to old bosses, giving you some cheaper ones while you level up, introducing new ones in the raids, garrisons, etc... Just super excited. Hoping I can finally get a huge barrel on my monk's back.
Edit- Now that I think of it, this should probably be in the WOD section.