Apologies, I can’t tell if you are being serious or satire.
I’m leaning towards satire but in case you are serious, IPv6 built-in encryption is IPsec using opportunistic encryption (which then relies on dnsec…), and it’s not built into all IPv6 endpoints. Nor easy to configure, debug or support.
WireGuard, OpenVPN, etc are easier for users to configure and set up than IPsec, and less chances of mismatched configs, unsupported cipher suites, etc.
As for NAT, that’s irrelevant to the reason for using a VPN. IPv6 has Unique Local Addresses (ULA), which can be routable across and organisation but not from the internet, and so you may want a VPN for access to those. You may also simply want to extend your IPv6 network to a remote location that doesn’t have native IPv4, or whose ISP doesn’t provide sufficient delegated subnet ranges for your requirements. The VPN could also be to provide access to an IPv4 network behind the IPv6 router. The list goes on…
I’m leaning towards satire but in case you are serious, IPv6 built-in encryption is IPsec using opportunistic encryption (which then relies on dnsec…), and it’s not built into all IPv6 endpoints. Nor easy to configure, debug or support.
WireGuard, OpenVPN, etc are easier for users to configure and set up than IPsec, and less chances of mismatched configs, unsupported cipher suites, etc.
As for NAT, that’s irrelevant to the reason for using a VPN. IPv6 has Unique Local Addresses (ULA), which can be routable across and organisation but not from the internet, and so you may want a VPN for access to those. You may also simply want to extend your IPv6 network to a remote location that doesn’t have native IPv4, or whose ISP doesn’t provide sufficient delegated subnet ranges for your requirements. The VPN could also be to provide access to an IPv4 network behind the IPv6 router. The list goes on…