Agree with manual overrides there is no reason to not have a key. I'm surprised you've read about that because that's against regulation in commercial security. If power goes down there should be a battery backup to power it and keep the key card / door security working OR it turns off and you can't lock your doors. Better to keep unlocked than have someone burn alive inside.
The beauty of IoT is how it can be easily expanded and connected should you choose to. There is nothing preventing companies from implementing the same idea to the payment system. Charge enough for securing those IoT devices once they reach out into the world and I think you can have a real system on your hands.