What kind of improvements do you think the 5DIII needs?
Well, as you see I don't own one (yet, still waiting for the price to drop or if it doesn't to get a used 5d2). But this is what can be improved w/o copying features from the 1d like spot metering on the af point:
* pop-up flash
would be nice but it doesn't seem to be their way for above xxD
there are some complaints about TSE and D700/D800, not sure how serious or whether that could be avoided
* non-crippled, faster sd controller - as it is sd is only good for jpeg backup and starting magic lantern
apparently that is just how their chip maker makes the interfaces and it wasn't any intentional crippling by marketing, maybe by the next round i'm sure, it will be different
* replaceable viewing screens
would have been nice
* well, for me: swivel screen (yes-this-is-very-useful)
could be useful
I think video is where they could've crippled it less, although ML is starting to fill in some of the gaps but better quality codecs, two crop modes, peaking, 100% zoom box live during filming, zebras, clean HDMI 1080p out, better histogram, etc. (ML does give better histogram and zebras and some degree of peaking already, not sure it will ever be able to give crop modes and who knows how far it can go with the codecs, etc.)