Hi Alex,
Very thorough write up, as always. If only this article was available some time ago when I was putting up an edge proxy, would have saved me weeks of frustration in figuring out all these NAT-related aspects and RFC readings (although such an exercise helps understand the problem to its core).
What you may consider adding to your article is the option of the yet not so popular, but in my opinion the "future of NAT-traveral" practice in IPv4 networks, which is the SIP Outbound mechanism.
Best regards,
--Sergiu