> Only the edge equipment would need to be IPv4+ aware.

"Only"? That's still the networking stack of every desktop, laptop, phone, printer, room presentation device, IoT thing-y. Also every firewall device. Then recompile every application to use the new data structures with more bits for addresses.

And let's not forget you have to update all the DNS code because A records are hardcoded to 32-bits, so you need a new record type, and a mechanism to deal with getting both long and short addresses in the reply (e.g., Happy Eyeballs). Then how do you deal with a service that only has a "IPv4+" address but application code that is only IPv4-plain?

Basically all the code and infrastructure that needed to be updated and deployed for IPv6 would have to be done for IPv4+.

But the desktop/laptop/phone/printer was the EASIEST thing to change in that 30 year history. And it would have been the easiest thing to demand a change req from a company for.