The next Nikon due for an upgrade is perhaps the D700, but I do not expect it until Spring of 2012 (Nikon 4 year cycle).
However, I am sure the D400 and D4 will be announce this coming fall.
I am hoping for the 12mp D3s sensor finds it's way into a new product. The new Expeed 2 processor is sure to be used. And, we can expect more advances in Video, hopefully 60fps recording and much better auto focusing.