BitTorrent has just released version 4.20 of their client and protocol. This version includes Cache Discovery Protocol. This protocol allows ISP to cache frequently requested file, and then clients on their network would prefer these caches, instead of the standard client seeds.
This will potentially save the ISPs external bandwidth, as most traffic will stay on their internal network. But I don't know if most ISPs will do this, or if they will just attempt to block this traffic. Also, once the clients are connecting with the ISP's cache, there will be a centralized place where the information about what files have been downloaded by each client. This will make it easier for the RIAA or the MPAA to subpoena these records.