Their idea is that RIAA or some such group could launch a "guilt-by-association attack" and create a kind of "mailing list" of users (specifically through the ISPs of users) to send out lawsuits. Your comparison to mobsters doesn't apply, because the threat isn't from law enforcement, its about rogue groups slapping civil lawsuits on people, in which case they can bring you to court on guilt by association- which sucks even if you're clean as a whistle.
However, you are correct in that so far no one has deployed this tactic, and SwarmScreen won't do much good unless large numbers of people start using it. Which involves accepting a performance penalty, against a vague and uncertain threat, without actually protecting the users identity.
IMHO it is less than proof-of-concept, it's an elaborate exercise in providing a false sense of security to torrent users. Its almost ugly.