Interesting idea. The proxy service would most likely be in the form of a "copyright agent" service for copyright/DMCA takedowns, with some degree of privacy protection for site owners. This would enable large scale monitoring of abuse.

The "act on their behalf" might be considered legal representation. As I understand (IANAL), the EFF as an organization doesn't provide legal representation to others, and more commonly refer them to a lawyer or law school clinic for further assistance.

Righthaven got struck down because they were only assigned "right to sue" and not ownership or exclusive rights to the copyrighted work.