What is meant by "rather inefficient"? Speed of serializing/deserializing?
I can't imagine that is a significant factor for communicating with bitcoin; if you're running into JSON-RPC bottlenecks (is anybody running into performance bottlenecks due to JSON-RPC yet? If you are, what are you doing?) then the lack of persistent connections, lack of JSON-RPC-2.0-multicall support, or bitcoin single-threaded RPC are likely much, much bigger issues.