Right now a new design of the free Spotify version seems to be rolling out to selected users, according to The Verge. A new feature in the redesign is the ability to play playlists on the demand. In the current/previous version of the app, every playlist could be played in shuffle mode. But now, shuffle-enabled playlists will be marked with a blue shuffle icon.
Spotify has said that they will present something mobile-related April 24th next week, and the new design will probably be officially announced there.