I've used twitchtv/twirp with success. I like it because it's simple and doesn't reinvent itself over and over again.
What about songle directional streams? Graphql streams aren't widely supported yet are they? Graphql also strikes me as a weird alternative to protobufs as the latter works so hard for performance with binary payloads, and graphql is typically human readable bloaty text. And they aren't really queries, you can just choose to ignore parts of the return for a rpc.