Good question. Sunmao focus on the UI part means it was designed to integrate any kind of backend.
And for FastAPI and other frameworks that provide OpenAPI schema, there should be a bigger potential to play with Sunmao, e.g, tables, forms, and other UIs that can connect to the API seamlessly.
As a personal suggestion, I think Sunmao is a little low-level(which brings great flexibility) to build such a kind of integration at this moment. It will be much easier after we provide some tutorials or examples of integrating with a backend framework. In the meantime, it will be appreciated if to join our slack channel and have some deep discussion.