My question/point is can that link be generated slightly differently once you visit it and then a new message gets added to the thread. That way it would at least turn blue again next time you visit the topic list to show a new message is in the topic someplace.
That seems like it could work. Perhaps as simply as adding the message count as a no-op parameter to the thread link. I don't know how many users might find that disconcerting though, as they may be accustomed to seeing the mark as "I've looked at this thread" without being interested in whether there's new messages in it.
The other factor is that I think a page refresh will be required to see the effect of a message being added to the topic by someone else. I don't think Groups.io's pages are dynamic in that way.
Could do that even without a specific app.
Could do any of this without a app, I think. I'm not sure why the inbox and the app are tied together in Mark's mind. Perhaps that has to do with infrastructure issues that I know nothing about.
To bring the idea to Groups.io's attention you are invited to post it in the group. That's the site's official suggestion box - no one from Groups.io monitors GMF. Maybe wait and see if any other GMF members have a thought on the topic first.