I don't really know, it probably depends on the scale. You'd probably want a CDN in any case. I don't know enough about torrents but I would imagine they'd be too slow to support streaming on demand.

As far as separating protocol/nip/whatever, I'm pretty neutral on that, except that media hosting is needed by nostr and if we made it "a separate protocol" that nostr clients had to support anyway it would just reduce adoption and not really solve anything. In the opposite direction, I'm not sure it being nostr or not nostr would matter to non-nostr use cases, it's just an interface people can use or not.