Manually selecting individual ranges / clips of a video will probably be more of a niche use case (imagine you have to do this for all your content to give your users a consistent experience).
As you pointed out, Plex will already autoplay trailers in place of the background art in certain clients / configurations. There’s an existing feature suggestion discussing for Plex to apply that to all content types (not just as part of Discover). Just mentioning this as a reference.
