No featured image functionality?
And you've defended this in other posts where it was requested by declaring that this not a "forum" function?
You are simply wrong. "Forum" and "Topic" are arbitrary terms for organizing posts. Everything on WP is a post. And posts can have featured images. A forum or a topic are merely a type of post that is tied to our other posts. And they certainly should able to have featured images.
For those who think they shouldn't be cluttering up a forum, you don't have to add one. How simple is that?