One of the reasons of #software:openengiadina switching to XMPP is the lack of C2S support / impls. See quote from openEngiadina announcement on C2S:
It may be a good time to see if there’s progress made since this discussion petered out… the ones leading the pack without too many platform-specific concessions might be ‘standard bearers’, so to say. I am really curious about @macgirvin’s take. And also where @lanodan and @naturzukunft got since this discussion started.