I think something like this may be good as a supplement to an online streaming service. Since the users who will take advantage of such a thing will generally be more advanced than the average viewer, I think this would best fit as a premium service (perhaps strip the advertising). Pay a certain amount each month and you can download the episode for later viewing.

This is the kind of stuff broadcasters should start experimenting with now. Stop looking for a permanent solution and try things out. Why do you think fast food chains have test markets for new products?