A musician may have a number of different playlists, perhaps designed for different singers who that muso might back. Those different singers might share some common songs, but they may each sing them in different keys.

It would be nice if those different keys could be stored and viewed against each song within the context of each playlist, so that song A would show as being in F on playlist Z, but that same song would show as being in the key of C on playlist Y.

For extra credit, it would be really nice if the charts automatically loaded in the nominated key based upon what had been recorded for that song within that playlist context.