Just dropping this here, but might be worthwhile to look at Tribler and what they have done over the years.
Its a torrent client build and maintained by distributed computing guys are Delft technical university (so Phd's master students etc, supposedly all well documented with accompanying papers).
The core of Tribler is the addition of onion-routing, but they (atleast for a while, maybe its in the background of removed now) have made a reputation/token system based on seeding.
Its a decent client regardless, highly recommend it other than that they recently ditched the standalone application and its is interface is now in the browser which i absolutely HATE :( .
tribler.org
