Oof, sorry. Bad reading fail there. Again though, you could you point me to something to read roughly how it’s used? That’s very interesting. I seem to recall Mike Hearn’s original crowdfunding project used that. I think I can vaguely imagine that helping, but I can’t foresee the details offhand.
No. Nostr relays’s main goal is not coinjoin. Almost 1000 relays that we can use to share PSBT.
The same is true of IRC; its main goal is not coinjoin, but users can just choose 1-3 out of many. It doesn’t mean it’s an ideal transport layer of course! 
No peer discovery. Discover yourself or run a relay and share.
Don’t really understand, you mean: the software exists and it’s up to users to find each other to do coinjoins? There’s nothing wrong with that, but it’s very limited; anonymity sets with unknown peers are clearly very desirable (and just as importantly, larger). If no, then I just didn’t get what you meant, sorry.