It is always a mystery how people just randomly misinterpret what I write. At literally no point did I mention port mapping.

I am pointing out how the problem NAT “solves” is just dynamic address configuration. They have implemented a N+K bit address where the N-bit prefix is routed and allocated using IP and the low K-bits are routed and allocated like a custom fever dream.

You can just do it all the same way instead of doing it differently and worse for the low bits.

To be clear, the router should rewrite zero bits in the packet under the scheme I am describing just like how routers have no need to rewrite any bits when routing to a specific globally-routable IP address.

You get a lease for a /N+K address. /N routes to your router which routes the last K bits just like normal as if it had a /N-M to a /N route. This is a generic description of homogenous hierarchical routing.