As much as I enjoy seeing Pandarens as a race it's not going to happen for quite sometime. Again, Blizzard does a pattern for their expansions, two new races, one new heroic class, two new races, one heroic class. It wouldn't be a smart move on Blizzards side to introduce one new race and one faction side heroic class. I couldn't even begin to explain all the issues that would cause. It would be beyond unbalanced.