I disagree with the premise of this thread completely. Piecing some information together it seems to me that the lore behind this expansion is essentially that tensions have built over various incidents involving the Horde & Alliance. They no longer have a common enemy to rally around, and already loose agreements fall apart as the only real enemy left is each other. All real outside threats are gone; or so they thought.
In their respective lust for war with and power over each other, they ignore something very important: Azeroth has been grievously wounded, potentially dying, and is, most importantly, vulnerable. All the while, the Void Lords and their Old God minions have been planning things in the background. Queen Azshara will rise again in this expansion as an actor on their behalf and will be a raid boss as Blizzard confirmed.
I predict that by the end of this expansion we will have some kind of Old God menace to contend with that will ultimately pose a far greater threat to Azeroth than the Burning Legion did this expansion, and it gets to such a point because we were busy fighting each other and ignored the signs of what is to come. Now this may not happen in this expansion per se, my thinking is it might be more along the lines of how WoD was a stepping stone into the Legion expansion. This expansion will probably set the stage for some kind of Old God/Void related expansion to follow.