As everyone knows, Nikon does not share info on future releases, but with what we have seen in new releases a D400 looks to be, mostly, a sure thing. Nikon is just working down the product line with new DSLR bodies D4/D800/D600 and the next one may very well be a D400. It seems that Feb/Mar 2013 will tell.
Then again, there could be an XMAS surprise. That would be totally out of the norm for Nikon, but it has been that kind of year.