There are a few problems with this. Firstly, very few users are going to cut down peak usage, because it's during primetime that they have the free time and inclination to use the Internet.

Secondly most people don't even know what a GB is. Thirdly, you assume usage-based fees are meant to curb usage rather than drive profits.

> or services would offer a way to cache episodes locally during the night so you can watch them after work.

Since we are basically talking Netflix here, this is never going to fly with the DRM guys.

This is not a technical problem, as you can see, since the desided outcome can be reached, if you are willing to ignore some legal niceties...