My thesis is that your p2p node could contact some other p2p node that's willing to act as a relay and create a mesh network from entirely within a browser.

If your side of NAT sucks and STUN fails, you'll probably only be able to connect to someone that has a NAT-traversal friendly configuration. But since you're able to reach them, they could act as a relay to the rest of the overlay network from behind your restrictive NAT.

Imagine I'm running one node that's willing to relay on a publicly accessible IP. If I'm the only node willing to relay on a public IP, then we've pretty much got TURN without the daemon.

If multiple nodes are willing to relay, then we have a general purpose mesh network within the browser sandbox that works on mobile?