For what it's worth, here is the letter I wrote to Canon back in November 2010:
I would like suggest an idea for the 5D Mark III and other future EOS Digital SLR cameras. It would be very nice to have the ability to be able to select a minimum and maximum range of shutter speeds, apertures or ISO speeds and have the camera automatically use those ranges as constraints for auto exposure calculation. Right now it is possible to force a single aperture via Av or a single shutter speed via Tv, but this is insufficient for situations where lighting changes rapidly (at a rock concert for example). The feature I am describing would be similar to Auto ISO except it would apply to shutter speed and aperture as well, and the range should be able to be set absolutely ("1/60s to 1/100s" for example) or flexibly ("1/60s or faster" for example). To be truly useful, all three should be settable together in a single shooting mode, enabling the user to set one or multiple ranges. Settings that are not selected would stay on "auto". This feature would provide a new level of customization that takes advantage of the camera's automatic exposure calculation while constraining it to exactly what the user needs. This feature would also be useful for people who want to maximize the sharpness of their lens, as they could limit the range of apertures to those which maximize sharpness and keep the ISO speed within their desired range. This would be a good mode to combine with Safety Shift in the event that the settings were insufficient to achieve auto exposure.
Please let me know if you have any questions regarding this idea. I believe it should eventually be incorporated into all EOS Digital SLR cameras as it would provide greater control over the creative process and allow for better pictures. It would provide an even greater competitive advantage for both Canon and its users.