Currently I have to create multiple public playlist, use the public api to query them, then compare results with previous results to see if a song was taken down. This makes for a very poor experience because I have to make useless playlists because favorites cannot be made public. Alternately I have to either write a complete server just to access my favorites, or use not so legal ways to obtain that info.
I think everyone hates when their favorite songs quietly disappears - happened to me many times. Fortunately I can obtain them again and upload them, but it’s very frustrating to use elaborate tricks just to monitor my library.