Christian,
Thanks for the suggestion. There's no way it would be a simple code change to make things work with the other network. It took us over 4 months to create the LinkedIn extension using JFBConnect as a base. The next network we'll be working on an extension for will be Twitter, and we're hoping to have that out in the summer.
After that, it would likely be Google+, but we'll keep xing in mind. We appreciate the suggestion, and are glad you're happy with JFBConnect.
Thanks,
Alex