Here's a summary of the pet-related Q&A, but check out Wowheadnews for the full transcript:
- Developers hope to implement experience gain from pet battles. Not enough to level just by participating in battles, but enough so players feel rewarded.
- Players will be able to toggle pet battle duel invites on and off just like normal duel invites.
- Players will be able to duel other players in pet battles, but there will also be a queuing system in which players can pet battle/duel other trainers of similar level.
- Pet battle combat = "simple combat system with some engaging depth."
- Possible pet battle spectating mode.
- Grasshopper pet is in the works for MoP!
Keep in mind that all of this is subject to change as developers continue working on the next expansion and the pet battle feature. We hope to hear more about the MoP pet battles and companion pets in general soon!