I find it inefficient to have an entire film download in the background when a user may close up at the 10 min mark. Either optimized download speed, or on-demand live streaming would be a better idea. Maybe there's a technical solution that could be developed by a startup in the issue - reduces YT's total upload amount, and saves money on both sides.
I think the problem is that the user may want to seek parts of the movie.
Maybe downloading just the next minutes and lowering the quality for a few seconds after a seek could help. Not so much wasted data and still acceptable seek time.