You have some proportion of power users that are outside NAT and WebRTC (they run a non-browser executable), their addresses can be shared over the network and

You have some proportion of power users that are outside NAT and WebRTC (they run a non-browser executable), their addresses can be shared over the network and stored locally. They provide STUN on rejoining, but are not hard-coded. (Overall, yes this whole thing is a vaguely bad idea. But not totally degenerate / non viable, just not practically worth it.)