IIRC Netflix are able to get around this problem by processing subscription payments outside of their app. Wouldn't this solve the problem for some use cases? Or has Netflix got a "special" arrangement with Google and Apple?
Netflix and Office 365 you buy a subscription and then you simply use the app on a multitude of devices.
As an aside - does anyone know if it's explicitly banned to buy "coins" somewhere else - and then use those coins to buy things in the app? This is actually how Epic games works.
Fortnite appears to offer a subscription. What would've stopped them from doing that when the game was still available on the app stores?