Actually, this unique cc # per merchant has been available for years. Different issuers call it different things (Citi calls it Virtual Account Numbers, for example: https://www.cardbenefits.citi.com/Products/Virtual-Account-N...) but it's not "automatic" like this sounds; you usually have to click on something to generate the number and type it into the ecomm site or whatever, and your card number never changes in this model. Check with your bank or issuer, they probably have something similar.

ApplePay and other phone wallets do something similar, generating new numbers for the payment but leaving the original number on the device or in the account. This is indeed more transparent to the user, but it doesn't give the control of capping or other levers.

Doing it via the card is clever, if that's what they are doing; if they are just doing it via the mobile app, that's somewhat old news... except for the other features, and the elegant giving of control to the consumer.