Well to be truthful I cant remember the last time I actually used ISO 100, the lowest I go in regular circumstances is 160, but my use does mainly lay between 160 and 640. I dont know why you call 100-400 dated, its still useful and I cant see a time that they wont be useful.
As for the range - with my Sony A700 they have different dynamic range options, allowing a standard mode or 5 levels of dynamic range optimization, or turned off. I've been able to use it to get what would have otherwise required an HDR composite. You can't say that tonal range is done growing, when you see things like HDR compositing gaining in popularity. Not saying that base level native tonal range needs improvement, but the ability to enhance the sensors ability to capture wider range.