@moshpirit Well, either it works as an XMPP client, or it works as an XMPP server. The latter is not going to happen, the first is a lot of work. Not saying it wouldn't be good to get more XMPP in the game, but there is a lot of work involved.
The quick 'n' easy method would be to just have a plugin to a popular XMPP server (like how quitter.es accounts also have XMPP) that also synchronizes your roster, somewhat like you described. But the problem you have to solve is - as always in federated environments - discovery: How do you _know_ there's an XMPP server on the other end? Why would the XMPP account be the _same_ as the remote instance's server? (and if it's not the same - are you really sure you want to straight-up publish your personal XMPP ID to anyone who's looking you up?)