In my opinion, the merchant processing/gateway revolution happened when providers (Stripe, Braintree, et al) started providing quality APIs for user/profile/subscription management and took the burdens of PCI compliance off of the companies building consumer products.
On the surface, I feel like this is a great way to offload the liability of storing sensitive user data -- though it also creates a central source of failure. Success is predicated on Luno securing their data; if they can't, the model would die.
If they can, it's possible we'll start to see a mass-migration of authentication-based apps switching to these service, if only for the legal intention of offloading liability.
Really, a fascinating model.