I think however, there are a lot of convenience, useability and build-quality aspects that need to be addressed. It is far from a perfect camera. A lot of the things perple are looking for in the replacement will make the camera more flexible, more accurate, and easier to use in multiple situations. I curse mine every time I use it and would certainly welcome a replacement that addresses some of it's failings -- even if we don't get more MP.
Strangely enough I don't have any issues with the 5D body at all.
I suppose the AF could be a bit better, but the whole 45-51 point business covering the same area as the 5D's 9/15 points seems rather pointless unless you're using AIServo to track moving stuff. Important if you need it but I could care less.
What I'd like is 5 high precision AF points, one in the centre and at each of the rule of thirds junctions with a quick select using the joystick.
I am also apparently one of the few photographers worldwide who doesn't use his camera in extreme weather conditions. The occasional bit of soft rain hasn't bothered my 5D at all. But the hue and cry over weather sealing completely amazes me.
I could care less about the LCD - all I want it for is the menu and checking the histogram anyway. How about making the viewfinder brighter and bigger and show ISO.
Not bothered about anti-dust. I haven't had to wet-clean my 5D sensor yet in a year of ownership, the odd blast with a rocket blower has been fine.
Not bothered about high fps. 3 is fine. I have occasionally hit the end of the buffer but I'm using a pretty slow CF card.
I would hate a built-in vertical grip, bigger batteries, etc.
Actually a camera with a next-gen FF sensor, in as small and light a body as possible (plastic is fine), basic but good 5-point AF, and a state of the art next gen sensor with even less noise and better DR than the 5D. More megapixels would be OK but not necessary.
In other words to heck with the feature list. Concentrate on IQ in as light and small a body as possible. It's not even a price issue particularly. How about the 1DsMkIII sensor with a single Digic III chip?