As a way to get Spotify working with Roon, could we use LMS as a source? LMS has a good Spotify integration so if Roon could control LMS it could then control Spotify. LMS has a good API so it would just be a matter of Roon telling it what to play. The trick would be how to redirect the LMS stream into Roon. Making Roon appear as a virtual Squeezebox to LMS.
Look at thread below for another approach that could work. And keep in mind that the (only remaining Logitech) LMS developer long ago announced that the libspotify API that LMS uses to provide Spotify is being shut down any time now (by Spotify) and when that happens Spotify won’t work on squeezebox devices. Look for mherger posts on threads on slimdevices forum on this issue.