Today we have 'Local files' that allow us to include, well, local files in our playlists etc. And this works well on my local machine. But as I have a home machine, work machine, my phone and my wife's phone these files are not available across them all. So I would love to see a 'Cloud files' feature.
Cloud files would allow me to upload/sync my local music online (either to Spotifys own servers or using a 'hook' to Apple/Google/others) and then those files would be equaled to music provided by Spotify.
I would clearly pay extra for this option (30 NOK pr. month?).