Transmogrification and reforging bots for engineers in Mists of Pandaria.
It might seem like a little trivial, given that these are just a matter of hearthing back to the city to do right there, but that's not always a good and viable option. When raiding, you don't have a ton of space to do things for only yourself, and you need to take into account the rest of the group's time.
Reforging pets, in particular, would be a boon for raiders. Often times, a new piece of gear can be quickly enchanted and gemmed (I know I always carry a few extra gems and enchanting mats on me when I expect to get a big new piece of gear); however, the reforging and "thinking time" (or Ask Mr. Robot time) that's necessary for high-end raiding isn't easily done. People can try to hearth and do it quickly during a scheduled break, but that's rarely practical.
Transmogrification pets would be less critical but would fit nicely into the engineering motif of providing unique gadgets and toys that provide at least some level of usefulness and/or fun. Engineers already have their own special teleportation generators and can make some fun pets and whirligigs. Letting them and others transmog their gear at a remote location, possibly through a Jeeves-like item, would be a nice addition to the engineer's toolbox.
So what say you, Blizzard, can we have some mogging and reforging pets, please? We promise to only transmog to look like Whitemane (and maybe the Stormwind or Orgrimmar guards).