It would be very useful to be able to add a short text comment for each songs that could be saved separately for each playlist (just like the key that is saved in the player). So the same song could have its own text info in different playlists.
For ex, I have a playlist for different singers, and some of the songs are the same in some playlists (except for the key). But some singer would sing a particular song a certain way, so it can be helpful to have some text info that could display some basic info such as solo order or a particular groove