Nobody ignored anything. To start with, the application community has had to work around these sorts of problems. This is why there are SIP proxy gateways, STUN services, and MX gateways. All of these exist due to connectivity limitations (either intentional or architectural).
It strikes me that most of the symptoms of the problem have the word "gateway" in the name.
Talking about policy domains, it seems that there is an implicit assumption that they are necessary. And that makes sense from a security POV. But policy domains do not /require/ site locals or NAT. It's just as easy (with v6...) to get global addresses and not route them outside the domain.
Then if you conclude that policy domains are a Good Thing, or at least Necessary Evil, then why is there all this talk to design a network that can somehow route around them?
My point is that A sends B a third-party address C, and the policy of the domain is "you can't route that outside my domain" then it doesn't matter whether C is site local, global, uses DNS, or whatever. Policy says it still won't route!
simon
-- www.simonwoodside.com -- 99% Devil, 1% Angel