Let’s look at another part of the lengthy comment Bob left after listening to the Rise of NAT podcast. This one is focused on the NAT traversal mess: You mentioned that only video-conferencing and BitTorrent use client-to-client connectivity (and they are indeed the main use cases), but hell, do they need to engineer complex systems to circumvent these NATs and firewalls: STUN, TURN, ICE, DHT… Cleaning up the acronym list first: DHT is unlike the others and has nothing to do with NAT.
A few grumpy thoughts on the mess called "NAT Traversal", the many standards to choose from, why IPv6 won't necessarily make things much better, and why the NAT pain is obviously not big enough to push people toward the IPv6 deployments.
Yet another blog article on IPv4, NAT, CGNAT, Hairpinning and native IPv6.