Some services allow you to add some songs currently playing to a playlist, the music library and some Amazon options seem to work if they use the queue. Haven’t looked at others.

I wonder how much background overhead would be involved in switching the source service between songs when playing? Again something I haven’t tried.

I'm not sure how that would work with Sonos radio or any service that does not allow you to create playlists or request specific song titles within that service.   The favorite’d (is that a word) would have to be saved to a play list on a different service.

I would absolutely love it Sonos radio allowed you to create custom playlists of songs heard on the radio though.  Even if that meant a song gets removed when it’s no longer in a station’s rotation...it would be useful.

It should be an easy feat: my local radio station allows me to mark songs as favorites and writes them in a simple, exportable *txt file. Easy!