It looks like from reading this one thread, that the only thing that's being nerfedon the AoE is for grinding. It's either 10+ or 12+ mobs, that the dmg starts to go down. Also Bliz has stated somewhere, that AoE's will be getting full +dmg to it. Here's the thread. AoE Change
I'd have to say, of all the "nerfs" the mages are getting, this shouldn't the one to complain about. Only during really large whelp pulls in the suppression room in BWL have I ever AoE'd more than 12 mobs at a time. I hardly consider that a nerf.