This is a great idea, it would make it impossible for any nongovernment entity to gather up lists of users to sue without opening themselves up to a lawsuit.

I had a similar idea that before receiving any torrent data each peer would have to send a message like:

As an agent of the copyright holder of works represented in aaaaa.avi, the user at [ip address] is working under my supervision and is authorized to distribute and reproduce the works contained in aaaaa.avi.