I personally use this rule to decide whether I should use a Google service/library: it has to have more than 1 billion active users or it's an important part of

I personally use this rule to decide whether I should use a Google service/library: it has to have more than 1 billion active users or it's an important part of such services. gRpc more specifically protobuf, imo, is very important to Google. So I won't be worried about its future.