A similar thought crossed my mind too. I've never used JSON-LD. I'm not quite sure where I would use it. One of the ideas was what you said.

The other idea I had is that it may help with transforming payloads from their serialized format into a static type system like TypeScript. It could be nice to have a system that can see an incoming response, validate the type using JSON-LD, and construct an instance of that object with it. It can be done without JSON-LD, but it may be useful.