Well, it's powerful because it's being used in the official product(music.apple.com). And you could use it for free(but not legally I guessed :D)because it doesn't have any protection to fetch it nor verification when using it.

I appreciate you are standing with us, but maybe there's more you could do now, not an uncertain "may be blocked at any time". I have a MusicKit related app on the Microsoft app store. As a victim of this unfair competition, I would like Apple could help contact Microsoft to remove that app (apps.microsoft.com/store/detail/cider-alpha/9P21XJ9D9G66) from the Microsoft app store.

@MobileTen Thanks for pointing out. But they still have a workaround, please see below.