When that happens we'll just share in a more localized fashion: directly between friends, at coffee shops, cafes, and public parks with wifi. Kids will do it in high school and college. True, it may be harder to directly share files with folks in say, Tokyo, but they are never going to be able to stop people from file sharing.
I work for a large ISP and even small municipality wireless networks are monitored for use and abuse.
College networks like the metro ethernet circuit at RIT that we run are monitored. File sharing from one dorm room to another is visible on our end.
1.- they already stopped
2.- the dl limit is already enforced in some isps, you just dont know it because you dont download enough and no im not joking
Actually benz, I do know about the bandwidth caps. I'm CCNA and CWNA. It's really not the download that you have to worry about either. You are more likely to get flagged for excessive upload. Penalties for distribution of pirated material is what they are looking for. P2P users often turn off their UL or lower it (bandwidth throttling) to try and optimize their usage. Verizon has a 5gb cap on their air cards, and Frontier is tossing around the idea of a 5gb total dl+ul cap for users not including packets used for services like online hard drive backup from Carbonite or movie dl from netflix. Time warner monitors packets and will cut your speed if you are a heavy downloader/uploader without even telling you.
Bitcapping is more popular with cable type isp's because the core network and access network are shared. DSL subscribers not so much because you are provisioned on your access line because it's your phone line...not shared like the cable system. On DSL only the core is shared. Most capping is done through the cable modems which are easy to hack and reprovision but if you get caught, your ISP will likely ban you for violation of their AUP or TOS. (acceptible use policy or terms of service)
Not very common for ISP's in the states at this point, but it's coming soon where you will likely have a 5gb cap and then metered service after...something like a per Gb fee past the 5gb included with service.
Most DSL and cable circuits are asymmetrical anyways which gives a lower ul than dl. I could go on about this shit but i'm at work right now and the last thing I want to do at work is talk about work.