this is my wishlist for 5D Mark III:
Autofocus 19/45 cross-type AF points - AF points spread all over the frame
I'll settle for 1 AF point that works with complete accuracy, 100% of the time.
Extended Dynamic Range
User Configurable Auto-ISO
Dual axis electronic level
IMHO, both are on the list of "definitely must have".
Bigger, Better and Brighter Screen
Dual card slots
Better weather sealing
Nice to have but I won't break my heart if they're not there.
What'd I'd also consider to be on the must-have list:
* 1:1 magnification for image review (I can't count how many times I've lost a picture because I thought it was focus'd properly/shake free in the field, only to get home and see, no, blurry...)
* "live view" magnification of 1:1 available, not just 5x and 10x or focus peaking for use with manual focus lenses
* focus with live view can be anywhere on the frame, not just within the invisible boundary
Oh... and for video (nice to haves)...
* 1:1 mode where only the center 1920x1080 rectangle is used with no interpolating