Nothing. Also nothing is stopping anti-virus companies from making their software detect the "Bundestrojaner" as soon as they have learned to recognize it. They have done this with the previous version, too:
Thanks. I wasn't actually aware they're a German company. This should make it even more reassuring though: if even German anti-virus companies won't give it any special treatment, this really makes it no more of a concern than any other malware from the user's POV (other than the political debate of course).