The expansion pack, which was unveiled at Blizzcon just moments ago but which wasn't yet dated, will include the new panda-like Pandarens. The expansion takes place on the continent of Pandaria and comes with a new level cap of 90. The expansion also brings with it a new pet battle system, new talent system, Blizzard's Chris Metzen announced today.
Metzen says that both factions can play as the pandas. It's the first time Blizzard has ever tried this.