Right, but NAT breaks those protocols now, and those protocols don't do IPv6 either[1].
Many do support IPv6 now, and those that don't either have it in their roadmap or could implement it if there was demand. NAT is a constant irritation every day for me with SIP. We do use SBC's, but NAT still causes problems from time to time when we run into a device that times out connection states incredibly quickly, or implements a highly restrictive form of NAT. Using NAT to free up IP space is only a half-assed short term quick fix: what happens when the next big application comes along that needs end to end connectivity and suddenly operators find they have to migrate to IPv6 very quickly? IPv6 is the logical progression, it probably is premature to migrate to it immediately, but there certainly should be pressure applied to hardware vendors to support it as this will make implementation far easier. -Scott