Comment by avidiax

The proposal is that IPv4+ would be interpretable as an IPv4 packet. Either the IP header is extended, or we add another protocol layer for the IPv4+ bits (IPv4+ is another envelope for the user payload).

DNS is like today: A and AAAA records for IPv4 and IPv4+ respectively.

Core routers do not need to know about IPv4+, and might never know.

The transition is similar to 6to4. The edge router does translation to allow IPv4+ hosts to connect to IPv4 hosts. IPv4 hosts are unable to connect to IPv4+ directly (only via NAT). So it has the similar problem to IPv6 that you ideally want all servers to have a full IPv4 address.

What you don't have is a completely parallel addressing system, requirements to upgrade all routers (only edge routers for 4+ networks), requirements to have your ISP cooperate (they can just give you an IPv4 and you handle IPv4+ with your own router), and no need that the clients have two stacks operating at once.

It's essentially a better NAT, one where the clients behind other NATs can directly connect, and where the NAT gradually disappears completely.