Let me give a "half full" view of this "half empty" glass. This experiment shows that not all UA to the right thing, but some actually do. If the "forwarded" scenario becomes important, user pressure and competition will drive more UA to improve their handling -- or more customers to switch to systems that handle such messages correctly. So there is some hope.
Since we already have ARC in the works to let lists keep working the way they always have, changes to MUAs purely to work around DMARC problems seem unlikely to me.
Regards, John Levine, johnl@xxxxxxxxx, Taughannock Networks, Trumansburg NY Please consider the environment before reading this e-mail.