I like Heraisu's idea. Criminals don't like to work in the light. Take the anonymity out of the equation, reveal who is doing the filesharing, and we'll just see how much pirating people are still willing to do when everyone can see that it's them.
I see a business opportunity in this: a central server that these hotspots use to authenticate users before granting access, and that also logs all traffic. To sign up, you have to swipe a ccard like you do to check in at the airport. No charge (or maybe there is) - just identity verification. Then, as you use your computer this site knows what you're doing and records it. If you steal someone's IP, it knows. If you browse kiddie porn, it knows. If you enable a student's web cam (well, you get the idea).
Several such companies could co-exist, getting paid by record companies to say who's downloading, and by police for other reasons. And because (a) this is on a public computer network which everyone knows is open for observation, and (b) the user would be asked to agree to this observation as a term of use with specific limitations (e.g. only to be used to identify law-breaking activities), it is done with the user's consent.
This could be taken a step further by separating the actual identities (e.g. name, etc.) from the identifying info (e.g. some ID number or CC number), so that users performing legal activities would not have their privacy compromised.