ranked in order of usefulness/desirability to me:
* Exe Control AF -> v2 ... improved to today's standards ... in conjunction with a top notch AF-system and a class-leading EVF on a FF mirrorless cam ... would be willing to pay up to $/€ 500 extra for this feature
* 1/500 or shorter X-sync ... implemented by means of a fully electronic shutter ... would only pay a little extra for it, since it is cheaper than mech shutter unit
* freely assignable Multi-Function ring around mount base on camera body ... default = aperture setting. As in Powershot S95/100 etc. Would be willing to pay up to €/$ 50 extra, since a hardware change is involved.
* Fully functional Auto-ISO including EV +/- compensation in "M" ... in any Canon EOS. I'd be willing to pay up to €/$ 25 extra, since no research / only a minor firmware change is needed
* A-DEP mode -> automatic depth of field. I would want the 3-step method [as implemented e.g. in EOS 3], not the latter 1-step procedure [as e.g. in 40D, 50D]. I'd be willing to pay up to 25 €/$ extra for that feature, since it reuqires a minor firmware change only. http://www.vad1.com/photo/autodof.html
* Focus trap -> automatic shutter release, as soon a moving object gets into [pre-set] focus. To my knowledge, this feature was never implemented in a Canon EOS - but on some/many Nikon DSLRs. I'd be willing to pay up to 25 €/$ extra since it requires only a minor firmware change only.
... lots of money to be made for Canon, if they build me a body with the desired features. Or even better ... Canon could leave out all video recording capability/features [except live view feed] on my camera and give me the above listed features instead, at no extra charge. 8)