I just updated the OS and the Music app. Happily, it appears the artwork issues are fixed and AppleScript can access the artwork data of a track (unless it's a file downloaded into the "Apple Music" folder). Additionally, playlist drags into and out of Folder playlists work as expected; it's just as tricky as it ever was in iTunes, but at least it's a sure thing.
There is still an AppleScript bug whereby delete playlist leaves a "ghost" playlist in the Sidebar until the next Music re-start. I have a few scripts in the pipe that rely on being able to delete playlists properly so this will need to be fixed before they can get posted.
Also, the reveal playlist command fails to scroll the selected playlist into view if it is not already in the Sidebar's view.
Otherwise, seems pretty solid.