Many, many Spotify users are getting incredibly frustrated at just being played things that they have heard before. Every artist or song radio ends up playing the same songs, almost irrespective of what the starting point was. It makes me want to give up on Spotify.
This constant repeating of songs works for some users who only want to listen to a particular genre or era. But for many others it becomes tedious beyond belief.
Why not let users choose how diverse their playlists are? They could dial up or down the degree of serendipity in being played new music. This would undoubtedly make Spotify users more loyal, rather than being driven away by the fact that a slight majority of people are unadventurous in their musical tastes.
I have written about the idea of the serendipity dial for the last 15 years and suggested it to Last.FM (which I still believe had a far better algorithm than Spotify).