Given Canon's 18mpx APS-C sensor technology, they can produce a 46mpx FF sensor without having to do too much. At the noise level of the 60D and if one were to downscale the 46mpx image to 36mpx (or 22mpx), I am very sure the noise level will be very comparable to the D800 or better. Shadow noise is a real concern for Canon however. Hopefully they can start putting in an on-chip ADC soon.
Sure, they can, but I think they have a proper reason for not announcing it. Maybe they are dealing with DR or something else ? Maybe they want to bring out fully operational product (with no AF flaws like D800) ?
Thirdly, DR. Perhaps someone can show me proper photos showing what those 3-4 EV advantage that Sony sensor supposedly boasts as compared to a photo taken with a Canon camera. I would be convinced then. Right now, all I hear is 'scientific' tests with a bunch of numbers. A proper set of photos would convince me what advantage a Sony's sensor has in terms of DR. So far, all I have seen is a bunch of numbers.
I want to see it too. Same location, same setup (lens, aperture, ISO, RAW). Then I can tell if there is so big difference.
If we look at the AF speed comparison on imaging-resource.com, it is very obvious that the 5D3 focuses almost 2x as fast as the D800 and do not suffer as badly from delays in buffer clearing, etc. That in itself makes the 5D3 a much more usable all-rounded camera.
Yes, 5D Mk III is more all around camera. Aimed mostly on pros, wedding shooters, photojournalist that require fast and precise AF and decent FPS.
So Canon should make a high mpx camera, by all means. Landscape and studio photographers would love that. It would definitely not affect the target market of 5D3 - People who need an all-rounded camera.
And I agree, there is market for high MPx body. It wont hurt 5D Mk III sales. Like you stated.