I think what me and @DZakh was talking about last is simply starting with GitHub - DZakh/rescript-openapi: 🕸️ Typesafe OpenAPI for ReScript, and leverage those types to generate ReScript Schema (Sury now) and ReScript REST for all of the contents. This would include emitting actual ReScript type definitions (records for objects, variants for enums/unions etc).
IIRC what we said was that it’s probably straight forward, just lots of work.
There’s also the alternative track of trying to take an existing OpenAPI client generator for TS (or some other suitable language) and adapt it to ReScript instead. Both tracks are interesting IMO.