That's not true. Spotify purchased an app that did just this by buffering into playlists that updated while they downloaded and then they promptly killed the ap

That's not true. Spotify purchased an app that did just this by buffering into playlists that updated while they downloaded and then they promptly killed the app. WatchOS 6 also includes the ability for third parties to stream directly and Spotify has publicly said that they refuse to use this until Apple changes their App Store policies. It's completely do-able and Spotify has the capability to do it, now and in the recent past.