I don't know about you, but I would rather that people respond by
stopping the outgoing spam run than by running around and trying to
unsign mail that's likely already been received.
Doug suggested that you can do this by making the revocation mechanism act
as a rate-limiter.
If a sender wants to rate-limit its mail, why can't it just do so?
John Levine, johnl(_at_)iecc(_dot_)com, Primary Perpetrator of "The Internet
Information Superhighwayman wanna-be, http://iecc.com/johnl, Mayor
"I dropped the toothpaste", said Tom, crestfallenly.