It would be very cool if there was an option so that Rockbox automatically changes the playlist after X minutes of music or after X songs have been played.
So after the limit has been reached, it would randomly chose a playlist from the Playlist directory (or from a list of playlists in a file?), then shuffle it and start playing the new playlist.
If we want to get fancy, it could play a transition jingle during playlist changes, randomly chosen from a selected directory.