I was reading some unflattering reviews of the new 5D Mark III but noted one that mentioned that we shouldn't come to expect huge amounts of improvement because we need to wait for each increment in the technology. OK, I can go along with that for things like getting better low light response, lower noise, higher shutter rates, higher video rates, and so on.
But there are some features I don't think fit in that category because they are more programmatic:
1. Allow a wider range of automatic bracketing choices, letting you choose how many steps above and steps below, and what the setting increment will be. For example you could choose 0 to 9 below, 0 to 9 above (yeah, 19 shots would be excessive, but you never know when someone might actually need that), and choose the exposure steps at 1/3 or 2/3 or 3/3 or 4/3 ... all the way to 9/3 stop per step. And not only allow choosing the bracket in shutter speed or in f/stop ratio, but allow diagonal and 2 dimensional bracketing.
2. More video frame rates. For example even the 5D3 doesn't have 720p in 30fps. At least all standard frame rates should be available (and both the /1000 and the /1001 rates for all models). But I also want slower frame rates, too. How hard is slower? Frame rates of 20,15,12,10,6,5... ? Why not all of them by having a menu frame to program in any new frame rate number as long as it doesn't exceed the maximum capable speed (which can then get gradually larger with newer models).
I'm sure I and others can think of other programmable features that don't involve scientific advancement, other than maybe adding some more memory.
Another feature I'd like to see is a true black and white digital camera. Take the 5D3 and make a new model the 5DM(3). The sensor will have no Bayer filter, leaving each pixel to capture the full spectrum. That will be a boost to sensitivity and detail. Programming changes would be needed for the firmware so it doesn't have any Bayer processing and works with only the single color channel. For RAW, identify only a single channel. For JPEG, either output a monochrome JPEG variant or (because some software may not handle it) a color JPEG with faked color coding with differences forced to zero. Unfortunately, this one would require enough of a market to justify it.