> NAT and CGNAT are not sins

Highly disagree. Middleboxes are a huge problem on global scale and have frozen any innovation below application layer. TCP and UDP even that they are on software not hardware layer cannot be updated or changed, see MPTCP efforts or QUIC giving up and building on top of UDP.

If this is so much privacy problem, IPv6 is there for many years reaching 50%+ deployments in some countries, I bet there should be concrete examples of such breaches and papers written.

> Reaching your own stuff is already a solved problem, too. Tailscale/Headscale

No address to receive communication - no problem install an app that would proxy it through someone who has the address.
Tailscale/Headscale is great, using it daily, but they are not solution to the huge already build global network created to connect devices not connecting devices because lack of digits. Global is key here.

My work guest WiFi network allows only IPv4 HTTPS on port 443 and their their own DNS. Everything else, including ICMP (ping) is blocked. Tailscale barely works as any persistant connection is dropped after 2-3 minutes.

Called this out and the security team said noone complains, that there is no use case and they do not want to deal with security risks.

And the ossification continues.