I've also noticed only Dwarf keystones are appearing on the AH, and nothing else since MoP.
I have sent two tickets to support but they both dismissed it as me being unlucky, although they both demonstrated they had no idea what I was even talking about. However anyone would know the chances of not finding a keystone after over 700 digs are extremely low.
If I am just being unlucky it should only take 1 person to get a NE, Tol'vir or Troll key stone to prove me wrong. Keep in mind that I noticed this only after finishing the Pandaria rares.