I think for this to be really useful I would have to create tight integration with some form of DB hosting so that the endpoints would be able to easily interact with the users data. Let me know what any of you think.
I post this in the hopes that nobody will snipe my idea but if you do at least invite me to help haha.
This seems both too hard and too complex to use for a non-programmer, and not worth enough to a programmer.
As a programmer, It's a lot of work to learn a new API. So learning something to rapid prototype that I have no control over? Why? I can throw up a Django prototype in a day that is going to cover my growing for a lot longer than an endpoint builder.
Just things to keep in mind, not to poop on your plan. It might be a really good plan. If you are serious about it throw up a marketing page and get signups to see if you can get traction.
See Hyperfiddle:
And also Vase:
https://github.com/cognitect-labs/vase
This is also similar to API mocking services.
Agree with other comments, it is important to find a customer.
Good luck!
More importantly, who is the customer? Companies w/o developers wouldn't probably be building an API, they would be looking at full services they can just pay for with a CC. Companies with developers can scaffold a REST API with some web development frameworks out of the box.
Who is the customer and what value does this SaaS bring?
How will you handle API authentication, rate-limits, scaling, analytics, etc.?
Sounds like you would have to do something unique, maybe focus on a certain niche. Maybe offer integrations to other services.
Good luck.