I tried this method on my test server too, but my users are strongly divided into email and web camps. The email users really don’t want to visit the web site to participate in discussions or reply to posters. They are going to continue to hit reply all in their email clients which makes the experience worse for everyone.
My Discourse site has login required enabled. Mailman didn’t keep email addresses private from the other list subscribers, so exposing them has never been a concern for this group.
Ideally I’d like to have the option to set the reply-to: header to the sender and provide a mailto: link in the footer that goes to the topic. That would keep the private replies off the topic, while still giving email users a way to continue the discussion without forcing them to use the web site.