[floatboth]

hmm. Multicast is often used for, like, IPTV. That's a very different task from BitTorrent. Torrents are indeed about managing peers. IPTV is centralized, not p2p, the benefit of multicast for IPTV is that the routers in between the source (ISP) and your client only carry one copy of the stream instead of one stream per client.

At internet scale.. well, it would be nice to have this efficiency for Twitch and YouTube Live. Which are also pretty centralized (CDN) so I don't see how this is about managing peers.

[opencl]

Bittorrent has a P2P streaming protocol called Bittorrent Live which was used to operate a TV service for several years but I have no idea how efficient it is compared to IPTV multicasting or central servers+CDN.