I like how everyone is just jumping to the conclusion that it'll be a dwarf expansion.
The Earthen of Khaz Algar are not dwarves. They are titan-forged who became affected by the same fundamental forces which were behind the Curse of Flesh, but evidently not to the same degree. So they're still Earthen, but they're breaking out from the Titans' fold to form cultures and cities of their own.
It's also not a given that they're the main theme of the expansion, but rather part of the main theme. We don't know if their contributions to that is "dwarf stuff" or "storm stuff". It may well be the case, for example, that Khaz Algar represents the element of Wind, while there will also be other new zones that represent the other elements.
That in turn could just be how Blizzard mirrors the new zones of Cataclysm, while a world revamp of sorts is also in the cards.
Like Keyboardturner on Twitter pointed out, Blizzard moved Kalimdor to make room for something. Khaz Algar might be there.
She's supposed to return to rule over the land, sea, and air. Not the cave, the dwarven inn, and the gryphon roost.