Without inside information all this is mostly speculation. However there are a number of general assumptions and observations one can make which seem reasonable to me.
(1) The major manufacturers, Canon, Nikon and Sony etc, probably have a fair idea of the type of product the competition is going to release next, unless secrecy is as tight as the weapons' developments of the US army, which I doubt.
(2) It seems reasonable to assume that Canon, with its own in-house sensor research facilities, will have various ongoing projects at different stages of development.
(3) They will have a road map of future releases and that road map will have a certain built-in flexibility, allowing for changes in priority according to changing market circumstances. For example, a 46mp sensor scheduled for release in 2 or 3 years time could be brought forward and released a year or two earlier, as a result of the great popularity of the D800.
(4) It would be naive to assume that Canon would have to start from scratch to develop a 46mp sensor. They've probably got currently a number of sensors with an even higher pixel count than 46mp, in various stages of development.
(5) Although the D800 has an impressively high pixel count which exceeds the pixel count of the 5D3 by a worthwhile margin of 60% or so, its high-ISO performance is no better than the 5D3, and if anything, slightly worse.
(6) For those who don't use a wide-format printer, 24" wide or wider, the 22mp of the 5D3 in conjunction with the 18mp of the 7D or 60D for long telephoto shots, is probably sufficient.
It would be interesting to see a comparison between the 7D and the D800 in DX mode, both cameras using the same focal length of telephoto lens of equal quality. The increased pixel count of the 7D, at just 3mp, would be insignificant in itself, but perhaps not insignificant when combined with the slightly longer reach of the slightly smaller 7D sensor.
In other words, using a 400mm lens on both cameras, the comparison would be between a 15mp image with an effective 600mm lens as opposed to an 18mp image with an effective 640mm lens. After cropping the DX image to the same FoV as the 7D image, we end up comparing approximately a 13mp D800 image with an 18mp 7D image.
(7) The undoubted advantage of all the recent Nikon cameras is the very significant 2-full-stops increased DR at base ISO, compared with Canon. However, to get things in perspective, those extra 2 or 2.5 stops of DR are not necessarily the solution for all scenes with a high contrast. If you are trying to capture an outdoor scene through a window and also want to include the interior of the room, you'll probably need more than an extra 2 stops of DR. You'll need to either use flash or take multiple shots for merging to HDR, whichever camera you use.
Nevertheless, I'm certainly glad I don't have to agonise over issues of whether or not to change camera systems. My modest collection of both Canon and Nikon equipment bought during the past 15 years or so, probably amounts in total to no more than the cost of a new, medium-priced automobile, but without the ongoing expenses of maintenance, fuel and road registration etc.
