I just cancelled my Premium subscription and wanted to give more accurate feedback about why I switched to Google Play and what Spotify could do to get me back because other than the lack of this feature I prefer Spotify.
Make the Spotify mobile apps an all in one music player so I can seamlessly go from my own ripped songs to downloads or streaming. The way the Android app is at the moment it is a PITA to add my own music to Spotify so I was forced to use another app for my own music and that means constant switching between Spotify and the Walkman app and no easy way to queue songs if I want to listen to my own music and Spotify music.
The Spotify app is my favourite music app and my only wish was that I could replace the Walkman app and easily listen to my ripped music with the Spotify app and until the day where every song I want to listen to is available on Spotify I will always have a need for this feature.
The Google Play Music app has this feature and is why I switched but I miss the Spotify app and I prefer Spotify so I'm hoping for this feature to be added at some point so I can switch back.