Just a random idea, I don't think I have seen it before, but I may have missed
it.
What about adding a checkbox in the mailman profile for subscribers of the
lists that basically says: if you detect that the sender is using DMARC then
please rewrite the From header.
This way everbody who is completely ignoring the silly DMARC stuff sees no
difference. And everybody who uses DMARC for scoring can still see the original
from.
People who receive the list on a yahoo account would have to mark the checkbox
(though maybe a list of default domains can be hacked in such that new
subscribers for those domain would get it set automatically)
It's a bit of coding, but it should result in almost no damage except in the
specific case of somebody on yahoo (or similar) receiving a post from somebody
from a DMARC protected domain.