This is an actual issue we are already experiencing in our internal usage. Looking through our community inbox (a group I do not belong to) is a pain due to the UI being in the “wrong mode”. We support cleaning this up.
However it is not slotted to a release yet, I anticipate this happening somewhere between 4 weeks from now to 6 months from now unless one of our enterprise customers pushes us to have this earlier.
For the record, messages exist as a filter under: /activity/messages in groups its just that the UI mode is wrong, it should display the same as it does under a user’s profile complete with the archived filter and a top level tab.