The speculation that higher MP automatically means more noise is not something that I am going to assume before the tests are in. When has Nikon ever released a replacement digital camera, especially at this price point, that ended up with worse noise that the camera it replaced, regardless of increasing the MP in the new camera. Obviously, its noise curve is not going to be as good as the D4, but that camera is twice as much money. But I'd bet that the D800 has at least as good as the D700/D3 when you down-sample to 12MP. So you can have a great low noise 12MP camera and a 36 MP fashion/landscape camera all rolled into one? This sounds pretty good to me. I have been living with 12MP for a long time and if they announced a D800 with better low light performance of a D4 @ $3000, I would think that was a good camera too. But as long as the down-sampled images are as good as the prior version, I think that this is going to be a big hit with many in the landscape, portrait and wedding arenas.
I still think that a D400 DX camera for sports enthusiasts and low light shooters who cannot afford a D4 will also be released.