If you use a USB async DAC, a Raspberry or similar device will sonically outperform PCs or Macs by a landslide, because of the different audio processing. The downside of using such a device with spotify is the clunky web interface, which can only connect to the Spotify Service via Core/Web API. Regardless, the sound quality is so much better, that i can never go back to the desktop clients.
If you´d open up the awesome spotify connect feature, you could offer an amazing experience for people who prefer open hardware solutions. Apart from politics/deals with manufacturers i can´t see any reason why this wouldn´t be possible.