Well, it seems people could sue the law firm, alas, the amount is too small, so the effort is rather high, even if it is likely that they win. But at least one person has already disputed the claim and sues over it.
And: Berlin public prosecution department has already started an investigation of the matter.
It seems they sent their applications to 16 different courts, most granted their application, but more than a quarter didn't. Such applications (regarding filesharing!!) are quite common and usually the request is granted.
Well, the case at least gets a lot of press and hopefully things improve.