NR has linked to a non-US forum which claims:
“Initial Information I received from a senior Nikon position in the USA, that Nikon D4 is already under primary field trial .FF sensor with 18 million pixels, Full HD-quality video as in Canon.
Frame Rate Of 10 images per second, 102,400 Asa quality similar to what today is Asa 25,600 in Nikon D3S. Improving the quality of the existing D3s by two stops.
Most important information: a completely new Autofocus sensor that will
enable outstanding autofocus performance. From what I understand, this is a real breakthrough Technology.
I was not told when the camera is expected to reach the market and what will be its price.”
While a D4 is almost certainly being worked on, having units out there being field tested when the D3s has only just started shipping seems a little soon... Also note some comments on NR point to a DPReview forum thread discrediting the author of the original post. Source: NR on 11/17/2009. | 
