I just stumbled on to this web site. Here is some interesting information on binning from Thom Hogan's web site: http://bythom.com/
It is towards the tail end of his July 13th post.
Here is what he had to say about binning and Nikon:
From Thom Hogan
Now for the part that, I'm guessing, could be Nikon's surprise in August: binning. Binning isn't new. The D1 was a 10.4mp sensor that was permanently binned (four underlying photosites to one pixel). Nikon has played with binning since then, too, with the oddly binned D1x (two side-by-side photosites to one pixel). The answer to the "why 24mp question" suddenly becomes simple if you add binning to the mix: you potentially get a D400h and D400x all in one package. I do know that Nikon and Sony have been working on binning recently. That would make some sense for both stills and video and could lead to a jack-of-all-trades DX body that excels at everything: low noise, high resolution, video without artifacting, etc. And it would explain pursuing 24mp in DX and 36mp in FX.
But I'm only guessing at the binning thing. Without binning, and especially without BSI, we just have more pixels which means more data and power lines cluttering the sensor, meaning less light efficiency. Thus, even with the normal expected gains of a new generation of sensors, 24mp wouldn't really get us much further than the 16mp DX capabilities we already have, if any. Plus 24mp by itself really is pushing the full recording of diffraction into most image data.
End Thom Hogan..
Well, if this comes to pass it means that my next camera will be a Nikon and not a Canon. Now if Nikon would offer flat-fielding I would have a great landscape AND astronomical camera!!