I know for awhile Netflix had this weird thing where you called a phone number and they would direct you to the Netflix website to sign up.
It's not having their own billing system, but allowing purchases to be made in-app that triggers the requirement. Which as far as I can tell, Netflix does not allow. I just checked and I can't change my plan in the app.
Maybe Patreon could leverage this loop hole as well.
You can view content from creators in app. But only patreon.com can be used to manage subscriptions to each creator. No in-app purchases on Google or Apple App Stores.
UX takes a small hit, but better than giving up 27-30% to Apple or Google.
It's not having their own billing system, but allowing purchases to be made in-app that triggers the requirement. Which as far as I can tell, Netflix does not allow. I just checked and I can't change my plan in the app.