Depending on the specific laws in Austria, being an exit node operator may make him as guilty as whomever was actually perpetrating the crime. Even if this specific case works out, governments in general won't take Tor or similar services lying down. For every privacy innovation, there is a lawmaker with the will and the means to destroy it.
As Tor becomes a part of more and more investigations, courts and lawmakers will begin to address the issues such networks present. Based on the unsavory reputation of the Tor network as a whole, prosecutors will begin arguing that the exit node operators know of the strong likelihood that they are enabling criminal activity, and will start asking juries to convict them as co-conspirators. If that doesn't work, they will begin lobbying their lawmakers to codify criminal responsibility for them.
As Tor becomes a part of more and more investigations, courts and lawmakers will begin to address the issues such networks present. Based on the unsavory reputation of the Tor network as a whole, prosecutors will begin arguing that the exit node operators know of the strong likelihood that they are enabling criminal activity, and will start asking juries to convict them as co-conspirators. If that doesn't work, they will begin lobbying their lawmakers to codify criminal responsibility for them.