Personally I don't see Nikon making a D4X, because the D800 already covers the territory, with the same reduction in noise performance that the D3X had versus the D3. The difference, of course, is that the D800 has the same extraordinary noise performance that the D3 had.
To get the maximum out of the D800's resolution, you either need to be shooting still subjects on a heavy tripod, or using studio flash. Neither use requires the D4's machine-gun like frame rate, and studio shooting doesn't benefit from high ISO performance.
In terms of being able to shoot and then crop, the D800 offers a huge advantage, whereas the D4 only offers a little more. That little is enough to make editorial shooters happier, because layout designers generally want the photographer to leave more space on each side than you would typically want when shooting pure photography. Nonetheless, the D800 is a different game altogether.