Is there any analysis of time of day/day of week usage and any movement towards differential pricing, i.e. unlimited nighttime usage with daytime/business day caps ?

Good analysis. However, there’s another issue which is perhaps even more important than duty cycles.

ISPs buy bandwidth in megabits per second per month, it’s true. However, when they determine how much they buy, they must look not at average or cumulative usage over the course of a month but rather the peak demand. If an ISP does not buy enough to handle the peak, the maximum possible number of users become frustrated with the service… all at once! So, the key measure of the effects of caps and throttling is whether it flattens the peak.