Spotify Connect allows users to play their music through other devices. However, SONOS (one of the most popular multi-room speaker systems on the market) is currently not supported in this feature.
Spotify can be played through SONOS speakers through the SONOS app, but the UI is very clunky and limiting compared to what the Spotify app has to offer. Integration through Spotify's Connect feature would offer a dramatically better user experience. Thank you!
This idea has already been submitted here. Feel free to add Kudos and comment on it to show your support! It has been marked as Not Right Now but Spotify might come back to it in the future.