I also find it interesting that no one seems to be pointing out that the 50D is very much iso limited due to its higher level of megapixels (noise/banding over iso 400) and the D3X and A900 seem to hit a barrier at higher iso's compared to their bigger pixeled bretheren. Of course the next generation will be better as technology advances but that technology will also apply to the bigger pixels relatively. The D3's sensor is better than the D3X and the D3s will be better than the D3Xs. The technology advances make 'pushing edge' sensors with limitations but allow 'normal' sensors with very few limitations. My point is that although later technology seems to improve on what was once barely acceptable at the pushing edge limits of sensor design, soon enough it might be time to stop pushing and just start consolidating.
In theory yes, but whether actual products emerge will depend on commercial decisions driving where Nikon wants to focus its technological investements.
The only domain where the D3 sensor is better than the D3x is high iso noise. On all other accounts, the d3x is better - and that includes DR, which shows that technological focus is more important than basic physical laws. Nikon decided that DR was key for the D3x, and they managed to get smaller pixels but much better DR still.
It was not obvious at all that Nikon would produce the D3 with only 12 MP in the first place, it took tremendous corporate bravery to stop the megapixel race and focus on better pixels, a move that no company had done before on a large scale for a live or die kind of product.
So I am really not sure that they will dare to do it a second time... bigger pixel might be a dying breeze, or to put it otherwise, I am not sure that the major investement in terms of technology will still focus on bigger pixels. Few if any of us have enough understanding of the very complex underlying technology to figure out whether optimizing a design/process for a 30MP FX sensor will have any actual benefits for a 18MP sensor.
My bet is that a very optimized 30MP sensor where Nikon will have invested 100M$ will have better high ISO noise than a 18MP sensor on which Nikon would only have invested 10M$, even if they are released the same day, because the technology required for the 30MP might not readily apply to the 18MP sensor.
Cheers,
Bernard