It would be nice to have an option to download songs, albums, and playlists that will be removed to free up storage space after a first listen / a set amount of time. This could be a generic setting applied to all music available online, or be an alternative option to the simple "Download" menu item.
It could work like for podcast managers (i.e. delete after the first listen), by automatically deleting after a set amount of time (e.g. 7 days), or a combination of the two (e.g. once I listen to a song / album / playlist, it will be removed after 2 days unless I play it again, in which case the expiration is delayed).