The only problem, besides the technical challenges of implementing an API, is how to market the API since new services get almost no traffic at launch and this is what eventually kills them. Without customers I'm just throwing money hosting an API nobody's using. 
You can offer a free plan that is slow. The free plan can be hosted on infrastructure that would be insufficient for paid customers. You could keep a copy of the required files necessary to implement the API in a storage bucket that can be accessed quickly, and spin up a more powerful server once you have a paid customer. Excellent idea, since I already have an AWS account. I'll see if I can come up with a mock implementation without paying outrageous fees on this kind of service that hasn't even been deployed yet.
