At first I thought gRPC/protobuf is not a transport protocol. Then I see that WebSockets has data framing and messaging. Is gRPC/protobuf light weight, though? What about Cap'n Proto? Or what about plain old UDP? I already see the bulk of relays have <50% connection success, so we're not expecting reliable transport are we? I guess UDP would mean reinventing some stuff. Again, I am speculating as an aloof user.
Discussion
grpc is lightweight, pretty fast, more universally supported than capn proto for other languages including javascript! and and gRPC's default transport is QUIC which is a UDP based replacement for TCP which aims at fixing "head of line" contention
if there is any candidate for an augmentation to nostr protocol it's gotta be grpc/protobuf
protobuf is the encoding, grpc is the protocol, it handles the request/response flow