Richard Fuchs, from Sipwise, has committed on a personal branch a version of rtpproxy control module that tries to follow the discussions held way back to develop a NG version that is more flexible and extensible:
The protocol use bencode instead of json as the format of the messages. A RTP relay application using this protocol is already available, developed by SIPwise.
You can see the full announcement at:
If you want to send your comments, join the discussion on sr-dev mailing list.