Airlines pretty much need to know their customers no matter how they get paid. Wouldn’t you just be moving that to another part of the process in that example?

API clients can already easily identify the user during the authentication process. What’s currently “missing” is a way for an API client to pay a service via the API call “on the fly”, without having a credit card on file or some prior account balance.

Maybe a better example is an image generation api. Your agent chooses one based on its research, and without any account or credit card on file, it buys you an image using a x402.