having multicast working on the internet would make this extremly efficient for the distributors (i.e. netflix) but the last mile (i.e. your ISP) still would have to deliver the packets to their customers one by one. at Netflix scale it would probably be already very beneficial to do that by broadcasting the stream starting every 5 seconds or something for uncached viewing. (i.e make the player wait for the next broadcast and jump to different ones [or start a new one at desired offset if none exist] when seeking).

Instead of using the internet its also feasible to use the DVB network like this. they could even broadcast a copy long before release so its guaranteed to be ready for offline watching when released. i am almost certain Sky Germany does something similar...