moderated Re: Groups.io Message Editor #suggestion
Re: "request to allow a sender to insert a "Reply-to:" header with an email address not subscribed to the list was granted."
I believe you are referring to this change -> https://beta.groups.io/g/main/topic/23242689#17656, If so, I don't believe it is germane to your request as this change only applied to mod/owners sending a message to an Announcement Only group in which Reply to Group does not exist. It's a very narrow use case where the mod/owner forwards a message received from 'somewhere else' and they wish replies to go to 'somewhere else', not to them. And only applied on messages emailed to the announcement only group, AFAIK.
The social contract of groups.io is still intact as the members of an Announcement Only group do not expect to discuss announcements, only receive them.