I still don't see why animating the exposure explains why there's "bad HDR" in games (high contrast and over saturation)? I haven't implemented it or read any papers on the subject, but the games I've played don't look that much different than auto-exposure on camcorders in the 90's (or your phone today). For actual cameras it's more difficult because you need to guess and adjust the aperture or shutter instead of having a HDR image in a buffer and deciding how to generate a LDR image to present. Calculating the exposure (especially if you're animating it and only willing to go so far in one direction or the other), should be fairly quick.