This is just a thought, and I may be missing something here... Why do the newest cameras have ever higher ISO figures? What I think would be better is to have a selection ofvery very low ones available to us. We could throw away our neutral density filters and have user-selectable long exposures, just by dropping the sensitivity of the sensor lower and lower. Digital imaging has no reciprocity failure issues to complicate matters with exposure, so why not?
Feel free to call me stupid! There must be a good reason that hasn't occurred to me!