[funny_falcon]

TCP can't multiplex. HTTP/2 runs over TCP and does multiplexing.

WebSocket can't multiplex. Nothing prevents gRPC over WebSocket implement multiplexing itself.

[jayd16]

Except it wouldn't work with a gRPC agnostic proxy. HTTP/2 can be split up by, say, nginx and requests can be handled separately. Any custom protocol probably won't have that level of support.