We've already established kernel cannot be accessed by third party apps today.
That's not the point. The point is that if Apple at some point decides to give kernel access to one of their products (e.g. Apple Music) they would be already required to also provide that access to third-party competitors of said product (e.g. Spotify).
There would be no "further step" the regulator would need to enact as the current rules already require equal access.