Google has removed unknown fields in proto3. I would love to hear the reasoning behind this choice. Also, if anyone has any way to replicate the proto2 behavior I would love to hear it.
If it matters, we are writing our code in Go.
As proto3 and grpc were developed in parallel, I wanted to reach out to the grpc community as well.
Source: Removal of unknown fields
Getting rid of field presence for primitives makes Protobuf more "natural" and efficient in many languages, since primitives in C/C++, Java, C#, and Go must be present. In such languages, if you want presence information you "box" the primitive by making it a pointer to a primitive.
Protobuf 3 gets rid of presence for primitives but still has it for messages. Thus, you can use the same "boxing" technique for Protobuf. Protobuf now has standard messages that box primitives.