Went to a panel at DragonCon today that was hosted by Johnathan LeCraft, a senior game designer for WoW, and one of his recent focuses has been pet battling. There' wasn't a lot of new info, but a few interesting tidbits. He repeated what we've heard many times now that they don't want to raise the pet level cap. It would invalidate all if the current pet trainers for end game pet content. But he did let slip that they're considering other things, including more quality levels.
He also mentioned ways to make takers more difficult, and talked about randomizing the encounters as one possibility.
What I did find surprising was that they have been planning pet battles all the way back to Burning Crusade days. Each time they added a new pet, it gave them one more reason to do it.