I think they lost me at "Foveon-like".
So it will have all the negatives of a high MP camera, like massive files to store, and a slowed FPS, and a faster-clogging buffer, but none of what you actually want from all those MP's, namely higher resolution and more detail to spare when doing things like shooting at high ISO, or cropping heavily.
Am I missing something wonderful about Foveon? If so, then so is everyone else based on the failure of Sigma's Foveon bodies to fly off the shelves. Why not copy FUJI sensors instead? That more complex, non-bayer pixel, no filter thing sounds much more interesting to me, anyway.
Your making a LOT of assumptions. The "negatives" of high MP cameras can be mitigated. With on-die CP-ADC (which canon does have a patent for), they can dramatically improve readout speed (they already proved they could read out a 120mp APS-H sensor at 9.5fps). With CFast 2 technology, we'll have faster write to memory, so the buffer won't necessarily be a problem. With Foveon, we get full color information at every single pixel, full spatial information, no longer need AA filters that are nearly as strong as is usually necessary with Bayer, etc.
Sigma's failure is that they market their product with lies and misleading information, and their bodies/firmware have never been very good (in comparison to Canon and Nikon bodies anyway.) Basing the success of ALL layered sensor designs on Sigma's success is a fallacy.
Fuji's 6x6 pixel interpolation is just another way of blurring high frequency data, only it is LESS effective than a standard AA filter. I covered this in very great detail in a long topic a while back, and the impact of the 6x6 pixel interpolation is quite obvious when comparing fine detail (i.e. hairs, telephone wires, etc.) between Fuji's X-Trans sensor and pretty much any bayer sensor.)
I could care less about what technology "sounds" more interesting. I care about what technology DELIVERS better results. Canon is a very conservative company...if they are going to move to a Foveon-like sensor design, then they must have solved some of the more significant problems that Sigma has encountered, and made it a viable design. They wouldn't bet on it if they hadn't. (And the chances hey HAVE solved many of those problems is very high, Canon has a couple patents on layered foveon-like pixels that use a different structure both for the photodiodes themselves, as well as readout; throw in their patents for on-die per-column dual-rate ramp ADC, and Canon could have a real powerhouse sensor in development that could really give the competition a run for the money...especially if it hits at a literal 40mp (i.e. 120 million photosites in 40 million actual pixels, not a trumped up 40mp like Sigma's Foveon.))