I think most of this discussion has proved that there is a need for 2 cameras. If we look at this from a business perspective, i think it's much easier to anticipate features and price points of potential cameras.
EOS "x"D Lineup 2012
1Dx - $6,800; 18.1 MP FF, 14 FPS, 61 pt AF, ISO 51200 Native, 2012
1Ds - $6,999; 21.1 MP FF, 5 FPS, 45 pt AF, ISO 1600 Native, 2007
1D IV - $4,999; 16.1 MP FF, 10 FPS. 45 pt AF, ISO 12800 Native, 2009
5D III - no price/specs released
5D II - $2,499, 21.1 MP FF, 3.9 FPS, 9 pt AF, ISO 6400 Native, 2008
7D - $1,400, 18.1 MP APS-C, 8 FPS, 19 pt AF, ISO 6400 Native, 2009
So looking at lineup shows me that there is a void between the the 1D and 5D which could be filled with a 3D which would probably feature ~25 MP FF, 4 FPS, 19 pt AF, ISO 12800 at about $3,999. This wouldn't completely cannablize the 1Dx bc it lacks the features some of the 1Dx market (sports) would be looking for, much lower FPS, ISO and AF performance.
Comparing across the line up also makes me realize that the price of the 5D III will most likely be in the $2,499-$2,999 range. Knowing that, it will probably feature 18 MP FF, 4 FPS, 19 pt AF, and an ISO bump up to about 12800 - 25600.
So from a business perspective.. the 5D III would get a healthy bump in ISO and AF perfromance over the 5d II. This makes sense, and considering the 1Dx stays is at 18.1 MP, I wouldn't expect a MP bump in the 5D III. Now if canon were to go for a medium format digital about 40MP, it would most likely intro above the EOS line at around $8,999 and price upwards from there. Canon has indicated that they have interest in develop such a product, but would not want to undercut the 1Dx or compete with that market.
SO.. maybe canon releases an M300 (made up name) at $8,999, with a new 40 MP sensor, 3.5 FPS, 9 pt AF, and ISO 6400.