This does not mean apps can now use alternative payment processing in-app. It doesn’t even mean apps are no longer required to offer Apple’s IAP in-app for purchases and subscriptions. All it means is that apps (in the US for now, but Apple really ought to make this worldwide, but I suspect Tim Cook wants to fight this on appeal in federal court) are free to inform users about offers available on the web, and to link to those offers on the web. Those links must open outside the app, in the user’s default web browser.