Music listening is completely subjective based on the smallest of changes within any given moment. Sure, the ideas of play strength/stars/constant radio/genre/BPM all helps in culling a mood, but it will never go all the way (without some sort of brain connection device).

I may create a playlist one day based upon a certain artist (with similar artists in the mix) however the next day I may want to listen to something a bit heavier, making those playlists irrelevant no matter how far I've drilled down my preference list.

While Play Strength is a good concept, it's still just a feature that can become just as underused or overused as a star count.

Instead of focusing on how 'perfectly-automatic' we can make a playlist based on features such as genre, BPM & play strength, we should be focusing on tools that help better understand our moods, the environment around us & the energy and vibes we intend to create from the music itself. The Effect > The Cause.