If you believe that "reputation" or "trust" systems might help the spam problem, then the only room for improvement is in the trust query protocol. DNS is a screw driver being used as a hammer in DNS blacklists. However, this is merely a matter of optimization or elegance.
I had some preliminary conversations with blacklist operators about this. There wasn't any interest in making a better protocol, but some people did expressed a need to document the existing one.
Yakov