One pet will be made untamable-- apparently there are issues with the Death Ravager that gets spawned in a quest in the lowbie Draenei area, Azuremyst Isle, and so hunters won't be able to tame him any more. Also, Petopia has PTR info on two new trainable pet abilities, Avoidance and Cobra Reflexes. Avoidance has two ranks and reduces the damage done to pets by AoE (this is aimed directly at endgame PvE pet viability), and Cobra Reflexes has one rank and increases attack speed at a cost to damage done.
As usual, all this info is still subject to change. But it's great that Blizzard is getting more and more pets (and pet abilities) in the mix. Here's hoping the trend continues.