XMMP is not private, metadata is exploitable.

Even if the data server is run by yourself?

XMPP is not a private messaging platform. It was specifically designed to be an open platform. Different components have been strapped on over time in an attempt to increase its privacy and security, but its foundation is simply not based on the notion of protecting user privacy. It certainly has its uses, but it shouldn't be considered an alternative to platforms that were built on the concept of privacy and anonymity.