The most that a signature can do is to identify the responsible party.
There's no point in adding cruft that attempts to go beyond that.
Given this why would any domain want their signatures to survive
transformations by mailing list message that their users send to, with
which they have no relationship and over which they have no control.
I'm with you. The stuff in some proposals that's supposed to survive
mailing list munging has never impressed me as being useful, even if you
believe that it works.
Domain Keys is only intended to survive forwarders like the the ones at
ieee.org and pobox.com, where any changes other than adding headers to the
top are basically MTA bugs and don't change the sense of the message.
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.