While Smart Playlists provide many features to control and randomize a set of music, it is difficult to provide the kind of granularity one might want when putting together a highly stylized playlist. You provide the ability to filter by individual tracks (Track Title), but it would be tedious to select 10s or even 100s of track titles for a smart playlist.
I propose a new a new smart filter parameter: Playlist. For example
Playlist contains xMy Favorite Dead Songs xEarly Beatles
Playlist contains xWorkout1 xWorkout2
The new smart playlist would be built on the contents of the playlists specified, as though each track in those playlists were specified as
Track Title is xTrack1 xTrack2 …
