The Horde already has Grimtotem, actually. It’s one of those things that got tucked away into the novels but after Baine retook Thunder Bluff from the Grimtotem with the help of Jevan Grimtotem, Jevan and about 1/3 of the Grimtotem tribe elected to follow Baine and join the Horde.
It’s a shame that we still don’t have their face paint as an option in the character creator.
There’s a Grimtotem NPC in Orgrimmar walking around near the Tauren AH.