An issue exists with cover thumbnails that don't have an aspect ration of 1x1 and therefore aren't square. For some videos only 4x3 or 16x9 etc. still frames exist on the web source and therefore the thumbnails and the hover images look very different, because they are streched and squeezed.
It would be very nice, if the cover thumbnails could be shown with preserving their aspect ratio.
Yes, nice idea and I've added this to my list. I'm also moving this to General Discussion and treat it as a request for improvement of an existing feature.