The side bar is not directly visible to users who browse on mobile, so the sorting buttons on top of the posts queue are more appropriate.
I think I didn't phrase it well enough.
I meant that somehow, users who mainly browse comments should be exposed to a few (5 to 10) titles of recent posts (new and/or hot) in that subverse.
Reddit, for example, puts a list of currently hot posts of the subreddit below the comment section.
This gives them some additional exposure.
The problem is the side bar on some subs can be very long and the list you'll end up being far below.
That why I mentioned the sorting buttons in posts and subs, they will give you a full list of posts sorted to your preference.
I see. It could be made optional per subverse.
But I have an alternative idea: Under the four sorting selector buttons, one could put a text that shows the number of submissions and comments during the last 24 hours, e.g.
7 new submissions and 134 comments posted during the last 24 hours
(post is archived)