Just a thought like that, but do you think it would be better if the actual appearance could be detached from a piece of gear that drops ? Having the cosmetic part only as a separate item. There would be no need for any restriction (like pets for instance), and maybe it would be possible to sell most on AH also (like cageable pets).
if rolling on it same restriction applies, only cloth can need cloth looks, plate can need plate looks, etc, other can pass or greed. If playing solo you get it account wide since they called it an account wide system.