The problem with this is that it requires hardware upgrades across the world: your computer, router, all the world's switches, a lot of software (e.g. software that stores IP addresses as uint32, but also native types that map to uint32), DNS infrastructure, etc. etc. etc.

This is basically the same problem as IPv6, except worse since we'll start from zero.

In hindsight, clearly a better plan than "this is IPv6, it's new, it's better, everyone will adopt it!" was needed for IPv6, and it would have helped if the IPv6 people were a bit more pragmatic from the start in their design (religious opposition to NAT springs to mind), but now it's about 20 to 25 years too late.