I wonder if the D800 sales might be pointing them in another direction...
I think the fact that Canon has not rushed a 36mp camera to market is further anecdotal evidence that the D800 series have not been an out and out winner for Nikon.
A high mp FF camera seems to fall into two very different camps. On the one hand you have a few serious photographers who really will be able to use that potential resolution in their work, and then on the other hand the casual user who gets most pleasure by drooling over the size of images at 100% on the computer screen. Pleasure may turn to disappointment when they find they have to use the finest glass, stop down a couple, mount on a rock solid tripod, crop out the edges of the frame etc, etc.
My guess is that when Canon do introduce their high mp offering it will be a very high end camera. Then when the consumer is educated enough to understand why a 18 mp 1Dx is five times more expensive than a 40mp 9D we might see a high mp 'budget' camera.
The great thing about the 5DIII and 1Dx is their image quality and frame rate. If we have a camera with a higher MP count, then the frame rate will drop. The current throughput for Dual Digic 5 is 225mb/s. This gives us a throughput which can be cut several ways, 12fps @ 18.1mp = 217mb/s. If we assume the same Dual Digic 5 chip set, 225mp / 5 fps 45 mp. If you want the higher MP chip then there's only one way the fps can go.
If the Canon develops Digic 6, generally a gain of 1.5x according to past upgrades, we get a potential figures of 340 mb/s, 12fps @ 28mp (nice) or 5fps @ 67.5 mp or 7.5fps @ 45mp.