Earlier quoted context omitted.
Risky, WebRTC isn't quite P2P, the sending peer still has to sort of spend the resources to send to all participants. It's a full mesh but you'd want something more open. You'll also have to consider DDoS protections for streamers.
I'm not sure what you mean... why would webrtc spend any more resources than the current solution?
For torrent P2P you get clusters of peers sharing data, you don't have to send data to every peer, the usual outcome is logarithmic, so you connect to log(N) peers for N participants with total bandwidth being log(N)M.