UPDATE:
Came across a set of model views from the Blizzcon Art Panel that included multiple colors of the yak!
This image appeared in a Mists recap/hands on playthough.
Since we typically see the "mount" animal in the starting zones of the associated faction, I don't think it's a stretch to say that the starting area is exactly the place to look for hints and ideas of what the Pandaren racial mount could be.
I think this ox/yak creature is an excellent candidate, don't you?