Interesting! When I first looked at gRPC I missed the option(google.api.http). Are you aware of the reason why REST mapped gRPC is not possible in GAE (http 1 only on the server end of our code)?
There's actually a stand-alone proxy that translates the REST mappings of `google.api.http` into gRPC requests. It relies on code-generation: https://github.com/grpc-ecosystem/grpc-gateway
This has been the way we've been shipping our REST services until now, but the need to recompile the proxy was a major hinderence to our development speed. Hence gRPC-Web implementation.
Google Cloud Endpoints, which released earlier in the year, allows you to write a gRPC server, and offers the HTTP proxy as part of the service.
The ecosystem still isn't quite there though. It could be easier to just write a thin webserver that just points at services over tcp (using something like ZeroMQ) rather than writing a service with gRPC from the ground up.
