I would see that easiest way to bring something like that would be some adaptation of m4u format, just instead of URLs to video it could have URL to torrent/magnet.

one issue I can imagine would be that each part would discover peers independently where assumption that most peers of previous parts should be expected to also have those files.

second idea would be to use ipfs in that way instead of torrent. that would probably have much easier time for reusing peer discovery between parts and also would solve issue when to stop seeding as this is already build in into protocol.

I guess that creating distributed twitch basing on ipfs would be feasible but not sure how many people would like to install ipfs node before that could use that. that's kind of chicken and egg problem, you need a lot of people before this system starts work really well, but to get interest it need to really perform well so people would migrate from twitch like services.

ofc you can use public gateways. afaik cloudflare have public ipfs endpoint that could serve as fallback