I tend to think that Apple should keep IAPs for actual in-app features but things like ebooks and video subscriptions should be treated like physical goods, where app makers can offer their own payment (and fulfillment). Amazon doesn't pay 30% for items purchased with the Amazon app, but it would if it offered Kindle purchases. This distinction makes no sense, since ebooks aren't app features or game gems or whatever. IAPs for such features make sense, since otherwise every app would just be "free" with pay-to-unlock and Apple getting nothing for running the store.