Hi. Hoverfly author here. I agree, messaging is vital in micro-services environment. We chose HTTP(s) as the first protocol to "virtualize" to help us better understand what additional functionality is needed (like hoverfly middleware).

The problem with 0MQ/RabbitMQ is that it's not that straightforward/transparent as in HTTP proxy. Initial thoughts to capture messages would be to use something like this http://api.zeromq.org/3-2:zmq-proxy as a forwarder.