Mark,
It's still a problem, at least for subscribers with certain MUAs.  I use Thunderbird, and the default reply action is always "Reply To List" even though the group is a [Announce-Only, Reply-to-Sender,Remove-other-options] group.  

Even though configured to omit all options other than reply-to-sender, GIO is embedding many headers which contain the group posting email address:

Sender: mygroupname@groups.io
List-Id: <mygroupname@groups.io>
Mailing-List: list mygroupname@groups.io; contact ...
Delivered-To: mailing list mygroupname@groups.io
List-Post: <mailto:mygroupname@groups.io>

Are all these necessary?   I'm suspicious of List-Post and Mailing-List in particular.  If these are not *required* by some protocol, it might be best to omit them for groups configured to not allow reply-to-list.  Ideally the post-to-list email address would not appear anywhere in the message in that case (perhaps it could be mangled so a human would know what it is, but no MUA could know the posting address).

I'll attach the actual headers from a message I received recently from our group.

Thanks.