”621 The Court also notes that in the but-for world where developers could use an alternative processor, Apple would still be contractually entitled to its commission on any purchase made within apps distributed on the App Store. Thus, so long as the alternative processor charged a non-zero commission or fee for its services, no economically rational developer would choose to use the alternative processor, because on each transaction, they would still have to pay Apple its commission, and they would have to pay the alternative processor a commission for its services.”
Basically the court recognised and affirmed that Apple can still charge their commission on all IAP - even if the IAP is not through AppleIAP.
So as a developer of a game with micro-transactions, I can offer a 3rd party payment processor.
But if I offer an alternative to AppleIAP then I still have to pay Apple the same amount and in addition I have to pay my 3rd party payment processor and do more work to integrate said 3rd party payment processor.
I strongly believe Apple will try to make this adjustment as easy for us developers as possible.
Apple will likely provide a new API we can use to automatically calculate the commission due to Apple as part of the method they facilitate for us developers to implement a 3rd party payment processor.
This will mean less admin for developers who want to implement a 3rd party payment processor. Apple may even require us to use this new API when implementing a 3rd party payment processor - to reduce admin their end. Apple will probably bill developers for the commission monthly.
If this happens the way I expect then practically nothing will change for consumers except we will sometimes have in our apps a more-expensive and awkward—to-use payment option as an alternative to AppleIAP.