One feature I've wanted on Plex for quite a long time is the ability to share a playlist with other Users or Guests and have it appear in their media players.
Usage examples of this would curated lists of Music, Movies, etc.
"List of Movies I think you might like"
"Top Simpsons Episodes"
If Playlist Sharing could have Parental Controls, we could block access using tags, allowing us to create Playlists for specific people.