Let's see...a FF camera with pro-level AF and 8 or more fps, more MP than the 1D X, and selling for 1/3 the price of the 1D X? And a partridge in a pear tree.
Exactly, that's not gonna happen.
I can see 5D Mk III like this:
1.) FPS: 5-6 fps max
2.) ISO: 100-25600 (even a native 12800 would work for me, expandable to 51 200)
3.) AF: at least 9 cross type points with center with higer sensitivity and ofc wider spread of them (really would prefer 7D style AF, but let's be serious, that's not gonna happen)
4.) Mpx count: Mpx of current is fine for me, no need for more
5.) Video: make it possible to shoot 1080p at 60fps
...and a useful thing would be if it wold be compatible with: WFT-E6A Wireless File Transmitter
and GP-E1 GPS Receiver
Thats my 2 cents.