Sonos has promised to deliver support for Spotify with Alexa voice commands on Sonos speakers by December 21, 2017. The company claims to make Sonos One a lot more useful product before the end of the year with this integration.
Currently, neither the new Sonos One (with built-in Alexa mics) or even a Sonos speaker paired together with an Amazon Echo Dot are able to start playing music from Spotify with voice command.
Alexa is able to pause, skip tracks, and adjust volume for music that’s being played on a Sonos system. So currently you can launch music from either the Sonos app or Spotify’s own app and then switch to voice commands for these operations. But being able to perform these operations using voice command will be far more convenient.
As of now, Alexa on Sonos can play music on command from Amazon Music, Pandora, iHeartRadio, TuneIn Radio, and SiriusXM. This December Spotify would be checked off as well.