[SamWhited]

That just means that some servers may have it built in (all of the maintained ones that I'm aware of do), but that you can still claim compliance if you support a general plugin system and delegate your multi-user chat implementation to an external plugin (because of the way it's designed it doesn't necessarily have to live on the same server or in process with the XMPP server). That seems like a fine implementation detail to mention and not a problem…

[jayd16]

You can say that..but it was a problem. It was not trivial, despite what the spec says or what is claimed now. If it was, more people would have used it.

[SamWhited]

I don't know what you mean "is a problem"; what's a problem, setting up groupchat? Everything uses multi-user chat and it's built in to all the servers I know of (but can generally be run as a standalone server if you prefer, which is what this means)? You can just enable it in your config and it just works on at least Ejabberd and Prosody, probably others.