This is pretty much what we have in DarkWallet (about the op comment and also specifics described by piotr_n).
http://coinjoint.info/dark-wallet-lobby-enables-secure-group-chat/https://wiki.unsystem.net/en/index.php/DarkWallet/Alpha3#New_lobby_featureshttps://wiki.unsystem.net/en/index.php/DarkWallet/Alpha2#P2P_gateway_channelshttps://wiki.unsystem.net/en/index.php/TrollNethttps://wiki.unsystem.net/en/index.php/DarkWallet/IdentityAlso openbazaar/darkmarket and our gateway's p2p network communication is building on similar concepts (
Trollnet document has more details).
For now we have implemented this using a different elliptic curve system (25519) than bitcoin, but everything can be done with bitcoin addresses in the same way, we just preferred the system to be considered without the implications of actually using a bitcoin address as your identity, anyways there are ways to link the different systems using signatures so web of trust, registrations or public key queries can work on different systems simultaneusly (this is what we aim, to tie our communication anon oriented wot, the btc and gpg ones too).
We have implemented some mechanics so peers can stablish links with each other in a similar way to what piotr proposes, calling them beacons and pairings (we also try to ensure identities never leak to untrusted parties). (
The Alpha3#New_lobby_features document describes the beacons and pair in more detail as well as private messaging, while the
Identity document has more implementation details)
The transport we assume is like an irc, although we don't need usernames since we don't ourselves identify users... that's all done client side. We also don't use irc atm since we needed to connect over websocket and irc is not specially suited for that, plus we had some operational/strategic benefits atm from using code openbazaar uses too and see where they go, and having the lobby together with other proxy services in our gateway (which is like kind of a bouncer too).
Our main goal at the moment is using the lobby/chat for coinjoin and multisig interactions, but also allows for irc-like conversations and private messaging.