Playlists currently lack interconnectivity and they require high maintenance when a user wants to have their songs aggregated/synced/grouped across multiple playlists.
Smart Playlist Concept Smart playlists (name is flexible) have the ability to track other playlists, allowing users to group and construct hierarchies from their playlists. Smart playlists would drastically enhance the experience of users that want to categorize their music.
Smart playlist features
A playlist becomes 'smart' when its owner selects another playlist for it to track.
Smart playlists can be assigned to multiple playlists and contain all songs from each of of those playlists (duplicates discarded by default).
Whenever a song is added or removed from a tracked playlist, that song is automatically updated in the smart playlist.
Songs can be added directly to a smart playlist and that playlist's tracked playlists would not be affected.
Smart playlists can track other smart playlists.
(Optional) Smart playlists can only track playlists created by the same user.
Common Use Case Consider a user that has many sub-genre playlists and wants to combine them to have a genre-wide playlist. Currently, that user needs to manually paste all songs from the sub-genre playlists into the genre-wide playlist. They would then need to manually keep track of whenever they remove or add a song to a sub-genre playlist and update the genre-wide playlist accordingly. For most people, this is too much micromanagement.
Smart playlists would enable this user to create a playlist that tracks the sub-genre playlists, seamlessly aggregating and tracking all songs from those playlists. This user could also add music that wouldn't fit in any sub-genre playlist to the genre-wide playlist without affecting the sub-genre playlists.
Smart Playlists introduce interconnectivity to playlists and empower the user to categorize their music in a unique, painless way.