Just to add another comment about this (I know there are tons!).
Sonos, please hear your users. Allow somehow that the Spotify App (and ANY app) installed on a Smartphone can play on the Sonos system.
That way, you (Sonos) won't have to constantly work on upgrading your own App to support the various music services.
I am sure Sonos Corp is aware of this -- from a business perspective, what is your strategic, legal, etc. reason for not allowing what so many users want?
Spotify within Sonos is about as terrible as a drinking a warm beer on the beach.