building a functionally useful decentralized reputation/rating network is a very big challenge.>

REALLY ? Torrent sites like cgpeers have a stealth reputation system without token and it works well for over 15 years. You can´t manipulate or buy votes=rep. there. If I can´t trust a Reputation score it is worthless.

And if everything depends on stake=money (not even linear) I can tell you who will win.