Long time full-home user here. Many (most?) of us listen to both our own Music Library *and* streaming services. The browsing experience is bifurcated, making it a bit clumsy and time consuming.
Yes, I can add streaming music to my Sonos Favorites and my Sonos Playlists ... but those are pretty "crowded" places. Enabling users to add streaming albums directly into their Music Library would be a major advancement is making Sonos a "unified" system.
The Music Library is already organizing by artist >> album. Imagine that I find "new" albums from an artist on a streaming service. If I could "drag and drop" the album from the streaming service into my Music Library, I could access it seamlessly. I would not need to remember which albums were located where.
This would be a huge step forward and continue to keep Sonos in the lead, as the best "all of your music" platform.