My idea as a user would be to be able to select from my web configuration page an option:
send_public_url_in_mail_footers: [ disabled, gmane_url, mailmanweb_url ]
And maybe it would be cool (if possible I have no idea) to add a mail command that when I send
subject: public $mailing_list $id
I get back an email with this url. Because maybe from one mailing list I'm normally not interested in the url and I also want it in some cases.
Not sure I anyone else in the world would like this feature though :D