> But it goes beyond firewall rules

Honestly though... does it, all that much? Even in a world where NAT didn't exist and we all switched to IPv6, we'd still all be behind firewalls, as everyone on an IPv6 home network is today. Port forwarding would just be replaced by firewall exemptions.

Like on a philosophical level, I do wish we had a world where the end-to-end principle still held and all that, but I'm not actually sure what difference it would make, practically speaking. "Every device is reachable" didn't die because of IPv4 exhaustion or NAT, it died because of security, in reality most people don't actually want their devices to be reachable (by anyone).