(news & commentary)
Nikon announced they will be showing the D4s at their booth at CES, but announced no real details. The camera will use the new EXPEED4 processor with some additional tweaks to how it works with the 16mp sensor in the D4 models. Also mentioned are improvements to the focus performance. We'll probably know a bit more in the coming couple of days unless Nikon is going to stick to the "behind glass" strategy. [Update: the D4s is indeed in a glass case at CES.]
With the Winter Olympics coming in a few weeks, Nikon's hand probably was a bit tipped: you can't really have an unannounced camera in preproduction form being used with that many photographers present without it leaking, so you might as well leak its presence yourself.
The actual D4s announcement will come in February.