Alliance players are killing two birds with one stone, here. They are encouraging a civil war that will doubtless end up with plenty of Horde, both pro and anti-Garrosh, meeting their deaths world of warcraft gold. They are using that civil war to weaken the Horde's defenses, so that in the end, when Garrosh is finally taken care of, the Horde that remains will be a much weaker one. And -- if the Alliance plays its cards right -- helping the anti-Garrosh side may end up in some kind of diplomatic resolution at the end of the war, placing the Horde in a far less threatening role.
Varian may not be the most present of faction leaders at the moment, but even he recognizes the wisdom of the actions taken by Alliance players in the 5.3 quest chain. In a way, it's a very sneaky build-up to what should be, ultimately, an Alliance triumph at the end of the Siege of Orgrimmar. It doesn't matter which way the fight goes between Horde and Rebellion -- all the Alliance has to do is wait for both sides to beat each other senseless, then move in for the kill. Check and mate.
So how do you tell a faction story while making sure the other faction is getting equal attention? That's a good question. I don't know if we've quite gotten the answer to it yet. But it's one of those puzzles that ought to be addressed, and it's a definite challenge in any kind of story development. Until then, we'll have to wait and see how the Siege of Orgrimmar plays out -- and what Blizzard's got up their sleeves next.