The pandaren are originally from central Kalimdor where they established the Pandaren Empire. They were allies of the night elves until they saw their obsession with magic getting out of control. The clans severed ties and left Kalimdor behind eventually establishing a new home on an island they named Pandaria. After the Sundering, some pandaren returned to the "new" Kalimdor to explore it. "Where once the pandaren were a mighty empire, standing proud beside their night elf allies, now they are a simple people who want only peace and a safe home." Since the Third War, more pandaren have come to visit Kalimdor.
Of course, this might turn out to be something else, like just another Warcraft novel, but I'm sure there's lots of players who'd love to play as the panda folk.
Source: MMO Champion