FWIW, I do very little "web work" (by which I assume you mean front-end?). Instead it is mostly api endpoints for mobile and server-to-server backend messaging. Lots of http transport stuff. If I were doing rpc, I would either not (and use a restful or type-2 api), or use something like protobuf or thrift.
Msgpack just doesn't seem, to me, as a really great fit for anything in particular.