Not to mention the software updates required to make it functional would exceed the software updates necessary for IPv6 _AND_ it has no lasting future.
Part one of that statement goes for v6 in a lot of places. The whole NAT444 allocation argument would go away with this. Maybe we need both. It might be easier to teach a v4-only device to use that space than to teach it to use v6. Part 2 is dead on in that it has no "lasting future" ... but what if it does? What if "Outer Slobovia" decides to simply number their nation using the entire v4 /0. Everyone can talk with each other inside the country just fine. $PROVIDER wants to provide services there? Well, they will just need to get an allocation out of Outer Slobovia's address space and NAT that to their services using either NAT44 or a stateless NAT64/DNS64 (Tayga or something). Outer Slobovia gets mad at the world? They just black hole the block set aside for foreign assignments and connectivity is instantly cut off. No v6 and no v4 leaks outside the country. I suspect we will see countries do just that.