I have run out of time to do any more outbound development before the freeze. I have added a page to the wiki here containing my notes on what is required to completely finish the development. I believe that the outbound support that will be in 4.0.0 will be sufficient for a Kamailio installation with separate edge proxies and registrars with flow-timer support.
I hope to be able to come back to this later (possibly not until late-February/March at this point) and do more work on outbound for the 4.1.0 release. However, for the time being - unless someone else wants to pick off the last items on the wiki page, I am parking this.