Anyone notice the D4 is expected to have 16.2 megapixels and the D7000 has exactly the same number of megapixels?
Does that suggest the new D4 sensor is essentially a D7000 sensor design scaled up from DX to FX?
If so, what would you expect the benefit to be from more than two times larger pixel size than is found on the D7000 sensor?
I suggest moving from DX to FX is good for a one stop improvement in clean high ISO simply because you are not enlarging as much so the noise spots are less noticeable when the same size prints are compared, such as a full page magazine photo from DX and from FX.
Second, I suggest increasing the pixel size two times will give you about two times more sensitivity to low light than in the D7000. This can lead to an improvement in dynamic range since shadow detail can be captured better.
Third, I suggest larger pixels will create a better signal to noise ration.
All in all I suggest the D4 will have more dynamic range and about a two or three stop clean higher ISO than the D7000.
This comparison with the D7000 sensor is not the comparison most people will make. They will compare the D4 sensor to the D3s sensor. I would expect more dynamic range and higher clean ISO than D3s simply because Nikon wouldn't bring out a new camera unless it was a significant improvement over the existing model. If not, no one would feel a need to buy it and that would harm Nikon's reputation.
Finally, the D7000 sensor was put into a less robust body, the D5100 and sold for much less money. Perhaps Nikon also can put the new D4 sensor into a less robust body and sell it for much less money? Into a D400 body perhaps? Or into a D800h body? I would like to see some sort of D4 "Lite" for those of us who want the highest possible clean ISO but don't need the robust build of a D4.