Numerous of posts by users on specific threads

[waccoe.com]

We've just upgraded from 3.4.8 to 4.1 and after initial howls of rage and pain have largely got positive feedback.

One of the biggest sustained complaints - oddly - is about a minor missing feature - the ability to click on a thread in the index page and get a list of posters who have posted on a specific thread, ordered by number of posts made.  We had this on our previous installation, but it was such a poorly documented original setup not sure if this was as a result of a core feature or an extension added in at some point in the distant past.

Is there something similar we could implement for 4.1?