My basic thoughts on the subject are mixed, the odds of me returning to WoW for this are minimal as most of the things that kept me playing (like my old guild) are gone, and it's a chore to really go through all of that again to be where I want to be. Not to mention the entire thing seems rather stupid and anti-climactic.
Don't get me wrong, the Pandareans have been part of the game lore, and we have had furbolgs (bear men) running around for a quite a while. What's more people HAVE wanted an unarmed combat class for a while. The combination of these elements in this way just doesn't seem to work, and the Jack Black movie has just made things worse.
Timing is also a factor, see when people were asking for Pandareans and such it was years ago and there were reasons for it. The game since expanded, added other things, and kind of changed in tone and content.
Most importantly is that the people asking for Pandareans kind of wanted they tossed in as this occasional cool thing, with them just being added into the races or whatever. A lot of it had to do with wanting another decent Alliance race to counterbalance some of the abillities the horde races were giving... an Alliance opposite number to the Tauren or whatever.
Extending this into an entire expansion pack is a big part of that problem, looking at that trailer what exactly do we have going on in "Mists" other than watching Kung-Fu pandas beat the crap out of people? What's more the idea is to relocate the entire game into the world of the kung-fu Pandas, and presumably keep the focus on it for the next couple of years.
When WoW came up the whole idea of a three way Horde/Alliance/Undead battle going on tied into the RTS game universe was awesome. The Burning Crusade which had people go through The Black Gate to fight demons was awesome and fit the lore. Lich King was epic, and brought about a finale to the ongoing storyline. Watching Illidan scream "you are not ready" or Arthas raise Sindragosa to the wistful narration of his father's spirit was epic... Deathwing in Cataclysm while justified by the lore was kind of "meh" and just didn't stoke me as I felt little real connection to it, and it was kind of set up to justify the developers doing some renovations. With "Mists" what we've got is some cartoony garbage involving a pseudo-asian culture populated by bear men, and little in the way of any kind of similar narrative structure to motivate me as to why I should really care. I wanted to fight Illidan and Arthas, Deathwing was kind of "meh" and that's when I left, I personally do not feel any need to return to WoW to get my butt kicked by a kung-fu furbolg which pretty much seems to be their selling point.
If you want my honest opinion, I think a lot of Blizzard's user bleed off has come from people just not caring about the game. Once the central storyline/conflict with Arthas was resolved, everything else has largely been drawing it out... rather transparently so. As some people have said, the game kind of lost it's soul after WoTLK.