However, I think that's part of why they've made this request. I think the problem is that it is late enough in the lifecycle of XMPP that no one large group (politically speaking - let's talk minimum of 100,000 people with similar political interests) really cares about it. That makes this not at all controversial, so it allows them to set a precedent.
I do not live in Germany, though, so I don't know if there's already precedent, or if the German people really even care about this. Hell, I don't even know if making XMPP service providers register is at all harmful or restrictive. All I can comment on is how it looks to me, and it looks like a power grab from over here.