I'm not anticipating a surprise army drop either, but what I will say is, if there were any plans for one it will have to come out before 4E no matter what it does to the schedule. It's why almost every new edition release has a crunch beforehand, all those new unit boxes, battletomes etc that were designed for one edition are not going to get "delayed" into the next edition, they will be pushed out instead.
That said, again, there doesn't seem to be anything pointing to chorfs or some other new army coming out in the next few months.