And if Canon take the nikon idea of an affordable FF camera capable of using EF-S lenses even better....
But Canon managed to put themselves in a corner now: If they revive aps-h or push ff downmarket, people who have invested in rather expensive ef-s lenses (17-55, 60macro, 10-22 or 3rd party ultrawides) won't be happy and might be inclined to switch to Nikon if they'd have to sell a good part of their lenses anyway.
I don't follow. EF-S lenses will still work perfectly fine on compatible cameras. One way to interpret what you're saying is that APS-C cameras don't deserve good, dedicated lenses, which I think is rubbish.
I think you over estimate the proposed Nikon D600. It is not a D800 or a D700. It will not have the AF drive motor in it thus meaning it will only work in manual mode with non AF-S lenses like the Nikon D40,D40x,D3100 etc. This will put a lot of buyers off as they will need to get their glass upgraded as well, as they will not be able to run a lot of lenses in auto focus mode, Nikon seems to have AF-S and AF-D variants depending on the motor drive being present in the body.
Lets see. If you've got a crop-lens for Nikon APS-C then you'll need to buy new full frame lenses for the D600 - no issue there. If you've never before owned Nikon, then you'll need to buy new full frame lenses for the D600 - no issue there. If you've been a Nikon shooter for many years and have not upgraded all of your lenses to not rely on the focus motor in the body, then you will have issues however those very same lenses will probably need updating anything to deliver the required IQ. So I can't see this being an issue. Really.
there is already a very nice one out. The canon 5d II. Which will be a very good camera for the years to come.
Isolated, yes, it will be a very good camera for certain situations. But as other cameras are delivered (perhaps by other manufacturers), the relative good-ness of the 5D2 will diminish.
Interesting points. I would guess the cheaper body would be deprived from many advance features, like alloy body, pentaprism viewfinder, awesome AF system, level of controls and etc., but retain the mk III sensor. Judging by this, it would probably cost similarly to 2nd hand mkII. I would perhaps stick with advanced features rather than slightly better IQ (my MkI is still good enough!).
If they reuse the 5DIII sensor in a cheaper body then all is lost and the camera isn't worth delivering. Now if they used the 1DX sensor, then that could be interesting but it may not sell well in that market space due to not having enough MP. But yes, the areas in which they can make cuts are in the FPS (slower/cheaper CPU), memory cards, alloy body, weather sealing and AF.