[Communitivity]

The marshalling cost might be negligible for come use cases, but the bandwidth usage definitely is not. I think the best interface description protocol is one where the serialization format is unspecified. Instead, the protocol describes how to specify the structure, exchange sequences, and pre/post-conditions. A separate document describes how to implement that specification with a certain over the wire format. That way the JSON folks can use JSON when they want (unless they are using large longs), and other folks can use what they want (I like CBOR).