I hope you didn't just throw https://github.com/postgraphql/postgraphql and https://postgrest.com/en/v0.4/ behind some closed source code and called it a business.

Words can hurt you know ... :) https://github.com/begriffs/postgrest/graphs/contributors?fr...

It uses postgrest but not postgraphql, actually not even the graphql-js reference implementation

Why? You don't think managing infrastructure composed of open source components is providing a valuable service?

That of course is valuable but it's not the main thing here. I'd say about 70% of the code powering this entire system is mine.

What is your business model here? Is this (subzero) projected to be an open source product supported by paid services and support, or is it entirely a cloud offering a la graphcool, parse or firebase?

It's going to be commercial, possible with access to source. You could run it on your infrastructure or have it hosted. Sort of like atlassian

No reason it couldn't be a mix of both.