Epic Games has filed a lawsuit [1] and published a Fortnite-themed parody of Apple's "1984" [2] to get some publicity for it.
[1] https://cdn2.unrealengine.com/apple-complaint-734589783.pdf
replies(8):
[1] https://cdn2.unrealengine.com/apple-complaint-734589783.pdf
If Apple changed their stance to "all services and digital goods associated with your app must included in the original purchase price", that might meet the court's requirements for legality but it would leave Epic without their current revenue stream.