I'm not sure I agree the gains are so small. Since automated order taking is already solved then once you remove the need to wait for customers to physically present payment you can largely remove cashier roles entirely unless one is requested by a customer. This also has a lot of interesting potential for servicing individuals who might be prone to losing money/cards such as the homeless. I'm all for demanding they retain the ability to take payment in more privacy respecting mediums but personally I'd find this wildly convenient.