The Tribler people have been working on some kind of incentive system so that you can download faster if you run a proxy. It's not clear whether that can compensate for the factor of N inefficiency that proxies create. BitTorrent only won because it was faster, so if a new system is N times slower than BitTorrent it's unlikely to succeed.

There's also OneSwarm which has been out for a while: http://www.oneswarm.org/