With 1.4.x, *.eml files were correctly attached with Content-Type message/rfc822. With 1.6.0, they are apparently declared as text/plain or text/html. Therefore, the message is not being displayed at the bottom anymore.
Bug or deliberate?
Might have better luck getting an answer on the RC github. https://github.com/roundcube/roundcubemail/issues
Didn't find any issue there which would answer my question.
The purpose wasn't for you to find an existing answer. The github issues page is where you can post about the issue and get a response back from the devs.
So what's the beef of these discussion lists
No one is forcing you to use github. Don't use it, just wait here on this list until someone answers you.
if apparently no answers can be expected at all anymore?
No idea, i don't work for roundcube team. You would have to ask them why they are not more involved in the mailing list.