The situation were this would be needed is having a collection of videos. In this case you may want to use the collection display fragment to display the videos.
More likely you would have a display page for the videos and on that page you would want to be able to render a video player using the video fragment. Currently this is not possible since we cannot map a video document to the video fragment.
More generally, it would be great to always make it possible to map content to configurations, not just to lfr-editable tags.