I'm the founder of WunderGraph. https://wundergraph.com/ We're doing exactly this. Our philosophy is simple, instead of forcing you into a specific stack, we can "introspect" multiple data sources like GraphQL & REST APIs, MySQL and PostgreSQL, S3 for file storage and OpenID Connect for authentication.

This way you can plug and play any of your existing infrastructure and services and turn them into your own private Firebase.

Finally, because we "introspect" all your data sources, we get end-to-end type safety. We don't just generate an API for you but also a truly type safe client.

Controlling everything from backend to API client allows for a lot of optimizations, e.g. the generated client knows if authentication is required to fire off a Query and therefore waits until the user is authenticated.

If you have any questions or feedback, feel free to join our discord: https://wundergraph.com/discord

We're going OSS 100% soon, exciting times ahead..