I have also heard such rumors of a supersized Canon system --- about every few months for the last decade or so! But so far none of them has been confirmed, and none has been backed by any persuasive evidence or arguments (hint: the arguments usually offered are no more valid now than back in the film era, and it never happened then.)
The whole marketing of Canon has been based for 20 years on leveraging the professional usage of their equipment (big white lenses at sports event) to attract casual shooters generating the bulk of their profit... against a single "enemy"... Nikon.
They are facing a problem now because Nikon has been threatening this approach since the day they released the D3 on 23-Aug-2007. It started with high ISO and has been low ISO image quality since the D3x was released on 1-Dec-2008. My understanding is that Nikon priced the D3x the way they did only to make a statement as a high end offering, they could have sold it cheaper but they wanted to release a body whose pricing would say "better than the 1Ds3".
We are at a turning point where many pros/high end amateurs are starting to really wonder whether Canon has the technology to compete in the high end segment of DSLRs. Whether they can still be seen as leading provider of camera delivery the highest possible image quality. Don't get me wrong, I know the 5DIII is an excellent camera and that Canon still produces some of the best lenses available.
If Nikon does release, as seems possible if not likely, a true 16 bits 54MP D4x early 2014, that will only further increase the gap and generate more boat shifting in the high end segment.
In that context, and assuming that Canon is still struggling to enhance DR of their sensors at the current pixel sizes, going to wider sensors may be they only technological option to remain credible in the high end segment. This is the exact same route that Phaseone selected by maintaining the same pixel size with roughly constant image quality per pixel, but increasing the sensor size to reach higher resolutions up to the P65+/IQ180/IQ280.
So it does in fact seem slightly more likely to me than it used to and the sole purpose would be to protect their image as a high end photography equipment supplier. IE, to win against Nikon. Most reasonable decision makers would IMHO have given up years ago on using inferior in-house sensors in favor of Sony parts, but they have not. That says a lot about the level of pride of some key people within Canon, and this pride may have led them towards the unlikely MF path.
Future will tell. As a photographer, I would love this to happen!
Cheers,
Bernard