I recently returned from some travel and had the privilege of sitting next to a optics engineer with a "big" camera manufacturer (didn't say she was with Nikon but I got that sense). Over the course of five hours we spoke about cameras, what it was like working in the industry and the current economic climate. Based on our conversation this is what I think Nikon might be up to.
There will not be a D400 nor D700X but instead a 24MP D800 which will likely have full HD and FX sensor. This camera will go head to head with the 5D MKII and its successor.
The D300s will eventually be replaced by a D500.
D500 , D600 and D900 are reserved for the next generation of cameras and should begin showing up in 2011 -2012 along with the D4.
The current D3 will be replaced with an upgraded version of the current D700, likely a D3H with a body of similar size to the current D700, 15 - 16MP and burst rate of 10fps and of course dual CF slots.
The D3X will remain in circulation for another 18 to 24 months.
We talked about a lot, all of which I convey here being from mental notes. To me everything sort of makes sense.
BTW....a new 70-200 is a certain.