Thinking about this more it might be neat as a speculative kind of API call. If a service doesn't implement something but listens for these things, it could be a signal to create the endpoints.

The other purpose I could see is for operations that have some uncertainty, like a CFD or hedge or bet.

OriginalSize

Yep. That's more less the argument Nick Szabo made long time ago (I love Nick's writing). However, I think it can be solved on the consumer/customer side, ie you can set policy for paying rather than making decisions per API call.

But it's a good point. Maybe paying for API calls  is not needed. I don't know.

phaedrus

bitcoin

L402 to pay for API access with Lightning

I think there's a mental friction aspect to this that meant it didn't take off.

Balaji made it possible with the 21 Bitcoin computer back in the day but if normie world is any signal, mostly people want to be billed monthly after the fact instead of pay first every time. The power of APIs is automation so the last thing you want to do is slow that down whatever the reason.