read through as much information as I could, as I thinking about an implementation involving TOR.
One thing stands out, and you must have a reason, why isn't relay mode enabled by default and then you disable it? as I see TOR has a number of similarities with torrent p2p. the different is onion routing and that resources aren't fair (you get as much as you give). can't see a reason why relay mode couldn't be default on, so any newbie users would increase speed and strength, but if there was a specific reason to disable it then people could.
think of it like this, in England there is too few people doing organ donation, as people are lazy and selfish, so it has been proposed / changed that it's opt out not opt in... problem solved. suddenly the deficit (lazy people, the majority) are not a benefit!
Can't think of a security reason against it... could you explain?