> Most cloud providers have created different proprietary APIs to expose lightweight services to the cloud.

True. However, in the case of Google Cloud Platform, the Protocol Buffer definitions for their services have been open-sourced here: https://github.com/googleapis/googleapis

There are two immediate benefits/possibilities: you can generate your own gRPC client libraries for GCP services and you can re-implement GCP services using their open-sourced interface definition. One example would be the Google Cloud Functions Emulator [1], which implements the service defined in the Cloud Functions service' Protocol Buffer [2]. You could deploy that Emulator somewhere for a sort-of "dev" version of the production Cloud Functions service, and the Gcloud SDK could talk to it.

[1]: https://github.com/GoogleCloudPlatform/cloud-functions-emula... [2]: https://github.com/googleapis/googleapis/blob/master/google/...