Thank you, Adam. Good questions...

I recommend gRPC to anyone who develops a closed set of private microservice APIs. They'll quickly appreciate the reduction in time to develop clients, performance, strongly typed resources, and first class streaming support.

If your APIs are public or accessed from a browser, then use HTTP1.1/REST. You could do this by writing pure REST APIs, or front a gRPC API with a proxy like the grpc-gateway or GraphQL

I'm not sure what will break the REST inertia, but I'd start with providing first class browser support for gRPC (see https://grpc.io/blog/state-of-grpc-web) and by encouraging everyone who builds the next version of their API to do so with gRPC.