I don’t understand the bonus question, and there are a lot of subtlties to multi-person secure chat. Does the user agent really have to be a web browser instead of, say, an ssh terminal? What do you expect to use instead of web sockets, in a browser?

On different occasions I’ve used irc or nextcloud chat, neither of whichis ideal. Plus ytalk but that is 2-person only. There used to be fairly busy discussion on the moderncrypto.org messaging forum but I think that is quiet now.

/u/positive_intentions@lemmy.ml might be interested too.