Few days ago I was trying to make a timelapse of a firework show. I went for a fixed exposure in every shot: well, it turns out fireworks can have a great and sudden dynamic range, so half of the pics are exposed just right, but the other half is way overexposed.
Now, I think even going to automatic exposure in every shot wouldn't actually help: besides the exposure flickering, the problem I see is that exposure is measured before shooting, and since fireworks are sudden, the dynamic of the scene can dramatically change between the measuring time and the actual shooting time.
Hence, I was thinking that maybe an exposure time based on how many pixels are reaching their overexposed status during the actual shooting would be a working approach. For example, I set ISO (or a range thereof), aperture, and a desired exposure time: the camera tries to take such a shot, but if overexposure (or a certain exposure value) happens on a percentage of the sensor pixels before the desired exposure time, it stops taking the picture as if the shutter was released earlier.
Maybe fancy DSLRs already have this feature? I'm currently using a P&S with CHDK installed: I can do great things (with unsatisfactory IQ and speed performances), but I didn't find such a feature. Technically, it doesn't seem impossible to implement, assuming each pixel can interrupt with an overexposed signal.
Am I dreaming of non-existing features? Does it sound useful/useless to you? It won't be useful in all situations, but at least in those where the subject is suddenly and unpredictably bright (just like fireworks, or lightnings).
C&C are very welcome, indeed exactly what I'm asking for ;-)