After spending some time looking over JIRA, forums and the various wiki articles posted by other interested parties, I've come up with my own take on the Remoting 3 API.
This document is not exhaustive. Also, please let me know if I've made any factual errors or anything like that.
The wiki article has been updated with more information about JCA integration, and changes to the API based on that and other bits of information. It's a fairly substantial change.