> Over 30 years after its introduction, IPv6 has still not replaced IPv4.

The protocols are designed to exist side by side. Don't use IPv6 if you don't want to or can't. At some point IPv4's will be extremely expensive and you might prefer IPv6 performance over 3 or 4 layers of CGNAT, but by then the Internet is going to be on complete lockdown and most of what you do will need to be business-cased, identity-verified, approved, authorized, and managed by your ISP on a whitelist basis due to security, so I have stopped caring.

Some things:

* By the way, there was this: https://en.wikipedia.org/wiki/6to4

* The 32-bitness of IPv4 (AF_INET) is baked in on a very low API/syscall level among all operating systems. If you're going to make changes there, you may as well just use IPv6 (AF_INET6) because most of the work is already done.

* Your scheme has a total dependency on IPv6 to work. The value add is unclear. It's easier for servers to enable IPv6 than enable IPv6+adopt this scheme.

* Your scheme isn't going to make IPv6 traffic use IPv4 routes. Routes and IP reputation are becoming complex because the Internet is cracking under the pressure of the current geopolitical situation plus the last 20 years of consolidation and centralization. It may not survive in much other than name, especially if more countries adopt a national-level firewall.