Why do you assume theres no good use case?

trpc, grpc, etc are all attempts to add schemas back into JSON. Swagger, OpenAPI, etc are attempts to add discover ability back into JSON-based RPC APIs.

MCPs fall in here as well, which attempt to add schemas and discover ability back in where our APIs aren't actually RESTful.

Schemaed data may be more accurate than structured. Regardless I'd be curious how you would consider something RESTful when it isn't schemaed data or discoverable via the data describing actions that can be taken.