Mists of Pandaria will have a renewed focus on the Horde versus Alliance conflict. As part of that, it's been revealed that Theramore, Jaina Proudmoore's city-state, will be sacked by the Horde.
Now, it's probable that, like most major storyline events, this will happen "off-screen", in a novel or comic, or maybe a cut-scene before Mists of Pandaria comes out.
One of the problems with this method is that it's never the player's fault that the Alliance and Horde are at war. It's always that angry Garrosh, or stupid Varian. If only they were sensible and intelligent, then all these problems could be avoided.
I think it would be better if the players were responsible for the destruction of Theramore. If they had their bloody handprints all over the ultimate trigger for the FourthWar.
Here's how I envision it playing out:
Garrosh Hellscream (questgiver): Lok'tar Ogar, Champion of the Horde, Slayer of Deathwing! The Alliance have held us back for too long. Even now their armies encroach upon our territories, and kill our soldiers. It is time for us to deal with the main Alliance stronghold on Kalimdor. Your orders are to sack Theramore, destroy their ability to threaten us, and eliminate their leader, the mage Jaina Proudmoore.
Horde Player: What!?! Are you mad? This is an atrocity, an act of war. It is stupid and short-sighted! I will not do this.
Garrosh Hellscream: I offer you this epic weapon, Champion, and this rare striped kitten. It is not just any kitten, it is a Kitten of the Horde!
Horde Player: Theramore will burn, Warchief! The men and women will be put to the sword, and their children enslaved. Also, I would also like a gemstone collar for my kitten.
And then we have a phased instance of Theramore like the Wrathgate, only the players would be treated as the champions of the invading army. The Horde player's object is to destroy Theramore. The Alliance players also have a similar questline, but their quest would be to hold the line as long as possible, and then evacuate and get Jaina to safety.
I think an event like this would get the players deeply invested in the Horde/Alliance conflict. And it would force them to take responsibility for the conflict as well, the blood on their hands, rather than treating it as something that stupid NPCs came up with, or was written in a novel that most don't care about.