Despite what many assumed from my original question, I was not in the least bit concerned about NAT's replacement as a pseudo access control at the IP layer. M

Despite what many assumed from my original question, I was not in the least bit concerned about NAT's replacement as a pseudo access control at the IP layer. My concern was the lack of control and independence from the global network when it is needed. This saves organisations and individuals a small fortune and provides maximum flexibility and convenience in internal networking. However, I have been doing further research and while NAT discovery and traversal is an uncertain area, and (of course) firewalls are the design intention for IPv6 access control, the core ability to have access to private unicast addresses within IPv6 is covered by RFC 4193 (Unique Local IPv6 Unicast Addresses). So, 6-within-4 protocols need only be around as long as 4 is the majority globally routable IP protocol, which may be for a LOT longer than people think, instead of being around because 6 lacks support for existing functions.