After watching the video of Apple’s event yesterday, I think I was wrong in assuming that they meant recurring subscription payments would be possible for apps.
It sounds like they only meant the functionality that was then demonstrated: buying add-ons from within the app. And Apple’s no-demo, no-timebomb policy most likely precludes the use of that mechanism to hack apps to behave as if they were subscription-priced.
I hope I’m wrong. But I don’t think I am. And I hope Apple reconsiders this option in the future.