As explained in this forum post (it appears it never got posted on wishlist)

https://discourse.webflow.com/t/cms-collection-list-get-youtube-main-video-thumbnail-by-code-tuturial-huge-time-saving/79435

Would be incredibly useful, currently if you want to create a collection of video posts, you have to manually generate and upload thumbnails for each item in order to be able to display them in a CMS list.

The code in the above forum post is no longer available. It would be great to get this implemented!