Overlay networks do not fulfill the performance requirement, and your comment completely ignores that aspect. Overlay networks would be perfect if we could. Who here would not use Tor if latency was as good as outside Tor? Who here would complain if Skype-like networks were decentralized? The problem with overlay networks is that you either have to sacrifice latency or decentralizedness to get them, and IPv6 does not - ergo, overlay networks can not solve the problem because they can't incrementally improve without adding critically negative aspects while doing so. Invent an overlay network which is decentralized and adds zero latency, and such network would easily beat IPv6.
As for NAT, you are making an Argumentum ad populum fallacy to counter evidential claims. NAT adds complexity to software design when it operates over the network. Proof exists for this fact through RFCs and large design considerations documents. There are also evidental proof that such complexity adds to the cost of developing software, with equal proof that increased developing costs means increased prices. NAT traversal for many services also adds bandwidth costs and increases latency. I have a hard time understanding the argument that increased development costs, higher latency, and more bandwidth would be neutral for the user. The fact that a large number of users, mostly limited to a single ISP, are content with higher costs and higher latency doesn't seem to me to be a good argument in favor of NAT.
Vast amounts of content are delivered today on overlay networks (again: we call them CDNs). Overlay networks have enabled the current scale of content delivery on the Internet. Your performance concern --- about an overlay design you haven't even sketched --- is worse than handwaving: it can be falsified even without asking you to clarify.
I wish you'd stop trying to make me defend the NAT service model, because that argument is extremely boring. My point, which I think sees overwhelming evidence from just a cursory look at the modern Internet, is that most users are not harmed by NAT. Innovation continues despite its pervasiveness. We should use the time NAT has bought us to come up with something better than IPv6, which continues to bake critical policy decisions into $60,000-$200,000 Cisco router and switch chassis.
As for NAT, you are making an Argumentum ad populum fallacy to counter evidential claims. NAT adds complexity to software design when it operates over the network. Proof exists for this fact through RFCs and large design considerations documents. There are also evidental proof that such complexity adds to the cost of developing software, with equal proof that increased developing costs means increased prices. NAT traversal for many services also adds bandwidth costs and increases latency. I have a hard time understanding the argument that increased development costs, higher latency, and more bandwidth would be neutral for the user. The fact that a large number of users, mostly limited to a single ISP, are content with higher costs and higher latency doesn't seem to me to be a good argument in favor of NAT.