[nyconyco]

Yes and no. The only production-ready of such a requirement is "MUC light". Basically, it is a very simplified version of MUC, that does not rely on user's presence. It exists in the MongooseIM server, in Smack library for Android and in XMPPFramework library for iOS, as well as in Mangosta iOS and Mangosta Android, two free/libre/opensource clients soon to be released. So it is ok to develop a solution based on this approach.

The "open extensions" is available here: https://mongooseim.readthedocs.io/en/latest/open-extensions/... We call this "open extension" because it was not accepted by the XSF, but it is very close to an open standard.