The Olympus OM-D E-M5 has a pixel density of 3.75 microns (4608 X 3456 in a 17.3 X 13.0 mm sensor).
If we extrapolate to a full frame Nikon DSLR with a 35.9mm wide sensor, we get 68 megapixels, or almost double the megapixels of the 36-megapixel Nikon D800 / D800E.
Why not? Those pixels could be put to good use as-is, or in “oversampling”. A 68-megapixel sensor downsampled to 34 megapixels (in camera or in post) would produce stunning results, as I’ve proven in my downsampling examples in my Nikon D800 review (downsampling the D800 to D3x or D4 resolution).
It’s coming, sooner or later, and probably sooner— Canon has to be quite irked at Nikon body-slamming them in the mid-range DSLR market, and we might just see such a beast from Canon before Nikon.