RegisterYourCamera.com claims: "An extremely reliable source for RYC has confirmed a camera being field tested by Nikon to directly compete against the Canon 5D MKII. This camera will be announced at the PMA show this year."
They are speculating that it could be the D700x or D800, so the source clearly couldn't give any specifics.
To compete against the Canon 5D Mark II, it needs 20+ megapixels, HD Video, and a price tag of no more than $3,000. The D3x sensor in a D700 with video for $3k just doesn't sound plausible so soon after the $8,000 Nikon D3x launch.
So could this be a new sensor? Could this actually be a Nikon D400 with video, coming in at a lower price than the 5D Mark II (but with a crop sensor?).
Given the lack of specifics, especially the fact they didn't know the name printed on the front of the camera, you can't put much weight at all behind this one.
Source: RYC on 2/2/2009.