In the past, maybe three or four years ago, I downloaded a mod here on vb.org. I don't see this mod anymore. This mod allowed to see a preview of the first image/file attach or youtube thumbnail of thread in forumdisplay. The preview is showing when a member hovered his mouse over the thumbnail of a subject.
It would be an interesting mod under vB Connect 5.6.4. I am not a coder.
Here is a screenshot on vB 3.8.11 :