> If BitTorrent knew network topology, it could act smarter -- CDNs accept BGP feeds from carriers and ISPs so that they can steer the traffic, this isn't practical for BitTorrent!

AFAIK this has been suggested a number of times, but has been refused out of fears of creating “islands” that carry distinct sets of chunks. It is, of course, an non-issue if you have a large number of fast seeds around the world (and if the tracker would give you those reliably instead of just a random set of peers!), but that really isn't what BT is optimized for in practice.

Exactly. As it happens, this is an area I'm working on right now -- instead of using a star topology (direct), or a mesh (BitTorrent), or a tree (explicitly configured CDN), to use an optimistic DAG. We'll see if it gets any traction.