The title is self explanatory. It would be very handy to enable Music Playlists containers as child of other Music Playlist Containers.
In the project i'm working on, we are using HUGE music playlists and this is a nightmare to manage, because
1 - You have to deal with a lot of music segments in the group editor, and you can't name music playlist groups, so this become very challenging to manage in the long run.
2 - You can't play a playlist from wherever you want (even for testing purpose) in the editor, so to test very big playlist, you have to wait a long time to test the section you want (or having the right random occurence), or you do another playlist for testing only, but you have to ensure you don't do any mistake in the copy/paste process etc... This should be a lot more easier to achieve.
Having sub-music playlists would solve this problems as you could insert sub music playlist in the parent music playlist group editor, juste like a regular music segment.