im pretty sure since 2 xpacs in a row, that we wont get a new race. and im about 100% sure we wont see a new class since those take forever and a day to balance out and work out all the kinks.
so im assuming that the next xpac will just be a straight "go level to 95" xpac. which is fine. if the questing is on par with MoP, then it shouldnt be too terrible of a grindfest.