Pets and mounts I don't think will work with AH. Maybe costumes/pilot-customizations - but this would necessitate a chicken before the egg.
Obviously pets and mounts wouldn't work in AH. My point is that other games
do offer vanity rewards for certain achievements, and AH has the capability of doing the same in different ways (i.e. custom skins, maybe custom arena text color, a "rank" title, or whatnot)