The WoW Facebook page has some interesting screenshots of a Quilen mount and companion pet, as well as a vague description of the two: "Tales of their existence will soon come to fruition in Mists of Pandaria."
Sites like Wowhead, MMO-Champion, and Wowinsider are already speculating that these two will be the MoP Collector's Edition goodies, the Imperial Quilen and the Lucky Quilen Cub.
Honestly? The pet looks more like a dog than a lion-like creature to me. Maybe a bulldog? One that has an overgrowth of fur around its neck. Or a puppy that's pretending to be a lion. Tricksy pup! I see through your lies. Lion-dog? More like a... lying dog. Eh, eh? No? Bad pun is bad. :P
Don't get me wrong, I think WoW could do with more puppy pets. It's just that this is supposed to be a Quilen, not a dog. Right?
This cross species combination has me slightly perturbed. I guess it's.. cute? I think it would look cuter if it was actually a dog pet, though. My brain just can't seem to accept that this is what a baby Quilen would look like.
I'm not sure what it is about this companion, but it just doesn't sit well with me. Is it due to the fact that it's so fluffy looking while its larger counterpart looks more stone-like and mythical/mystical? Possibly.
In any case, I'm quite interested in hearing more about these two in the near future. With the news of Blizzard releasing the opening cinematic for MoP in August, the details about the MoP CE will likely be coming "soon" too.