Also don't ever forget you have the world's most powerful anti-DoS tool already implemented: micropayments.
I agree it's a powerful anti-DoS tool but with great power comes great responsibility. We like to prioritize UX over "slapping fees on something and calling it a day". Micropayments are not our revenue. They only exist to enhance the SN experience.
Why not just get rid of the API keys and charge users sats for API calls?
This would only charge the users who don't know how to use the API for free like the frontend