That is good to know. Do you have any recommendations for a more mature version of grpc (cross-platform communication with a high speed encoding)? Thrift?
You get load balancing and discoverability for free, since NATS will distribute messages equally to consumers: Just fire up new consumers, and they will get messages to the topics they subscribe to, and all a client needs is the host/port of the NATS server, which is going to be the same for all parties. Couple that with some hand-coded serialization — Protobuf, Msgpack or even JSON — and you have a fairly resilient, fault-tolerant RPC.
You could trivially do streaming RPC if you handled the request/response matching yourself — if you look at the clients, NAT's RPC is all handled on the client side, using ordinary messages with a unique topic name generated for each request/response. Extending it to support multiple replies per request would be simple.
There are other, more feature-rich message queues, of course, such as RabbitMQ. NATS' advantage is that it's extremely simple.
Another option is ZeroMQ, but it's a bit lower-level and doesn't solve the discoverability part. You'll end up writing much more glue for each client and server.
[1] http://nats.io