It does not look that hard TBH. Peertube already supports webtorrent and works quite well. Just fork Peertube, remove all the federation/fediverse crap, replace it by fetching magnet URIs for each video from nkstt events queried from relays, and it's done.

Peertube still host and serves the video on a single server. The average at home hosting person might have one gigabit up and down. Which would serve a maximum of 200 people a 720 p video. Make it only torrent based and that number would scale infinitely really. But you would have to wait a while for each video to start. Which I think is a fine compromise.

vigilante.tv uses the foss hive-tube plugin on their peertube server and it includes a magnet generator and the ui for it is on the download modal if you want to download a video. the torrent support is amazing.