[solidangle]

This technique will remain useful with IPv6. NAT will disappear, but the stateful firewalls (which are often combined with NAT) will remain.

[api]

Yes, but IPv6 helps a ton. Hole punching with IPv6 is almost 100% successful as long as your firewall allows it (and most do unless you are whitelist-only). IPv6 kills symmetric NAT and over-provisioned NAT.