I don't know if unlisted videos/posts are possible due to the nature of this blockchain system; you can't really hide anything that has been posted to the blockchain, which brings me to think that someone could make a service in which users could preupload their video to them and designate a time of upload to the steem blockchain, and the service would fulfill their upload according to the time and settings that the user designated. Hmmm. Good idea or not? If I were a developer I'd try to get something like that rolling and get a percentage of the earnings :)