I also had the thought of a logarithmic scale, like reviving the old German DIN scale. But maybe a simpler modern option would be to talk in stops of speed; say stops over (or under) 100. ISO 102,400 is just +10 over ISO 100.
An "ISO" scale that now reads ISO 50, 100, 200, 400, 800 ...
could be replaced by
a "sensitivity" or "exposure index" scale the reads -1, 0, +1, +2, +3 ...
This could simplify reckoning of reciprocal exposures: "I want to close the aperture down by two stops, so have to up the sensitivity by two stops".
But Jonathan W. might well be right: the only scale of powers we are likely to see are the slightly ill-fitting powers of 1000: ISO 12K, 24K, 50K, 100K ...
I severely doubt that ISO 102,400 is accurate to all digits anyway.
P. S. Whoops, I just saw Wayne Fox's post on the same idea. So .... Great suggestion, Wayne!
P. S. I would also be happy to dump the strange system of naming sensitivity by the acronym of the organization that publishes some standards for this, amongst thousands of others. For example, "ISO 9000" is not a film speed, it is a quality management standard!