Nikon Rumors has released a story about the Nikon D5. None of our sources have been able to confirm for us the inclusion of 4K video. The video on the Nikon D4 was disappointing but the video on the Nikon D750 was better than expected (for 1080P). Given that Nikon is in a tough position financially we hope they have decided to innovate rather than iterate and produce some good video features.
What does appear known is the resolution of 20.7MP (5568×3712) and an improved autofocus system with more autofocus points. The maximum frame rate is thought to be 15FPS.
As soon as we hear about 4K on this camera we will let everyone know. Unfortunately the price of this camera could be as high as $6999 (we are hoping for $5999 given what the current strength of the US dollar).