The ISP transforms torrent files on the fly to serve local seeds to its customers.

But this should be done by the torrent client instead.

Torrent clients can count hops between various seeds served to them by the tracker and try those that have lower number of hops first. That way, the client is likely to try seeds from the same ISP.

To avoid traceroute of each seed (there may be thousands), the discovered topology information could be shared with other peers so that there is no need to do traceroute one more time. For example, the number of hops between 1.2.3.A and 4.5.6.B is likely to be the same as the number of hops between 1.2.3.C and 4.5.6.D – assuming the prefix /24 is the most common.

If the torrent client can guess network topology information by itself, there should be less needs for local trackers or technologies like P4P. The torrent crowd could map the Internet this way.