I think you are missing the point here. The Copyright Alert System is solely concerned with bittorrent peers, and, as I was able to get clarified via a question during the conference, only to seeders and not to leechers.

The actual monitoring will be done by Mark Monitor on behalf of the content companies. If they successfully leech identifiable content from a seed, then that seed's IP address will be passed to the ISP for CAS processing at the appropriate alert level.

The ISPs will not be doing any monitoring under this system..