Every expansion either introduces new races or a new class. With the race developers concentrating on new models, it appears that it is up to the class team to create the showpiece for the next expansion. As everyone knows, it takes something major like 2 new races or a new class to push a new expansion. We also have the 10th anniversary of WoW to consider as well.
In other words, I just don't see what else they could do except bring out a new class. The race team will more than likely be too occupied to create 2 new races. Even though Monks just came out, Blizzard may not have a choice but to bring out a new class in e next expansion.