[welterde]

I don't think that plan is feasible at all.

The incentives for vendors to implement it are just not there, since the customer is not actually going to use the expanded address-space feature at all for at least a decade, so why bother implementing it and break the existing stuff in the process? While with IPv6 you could at least somewhat use it right away or at least implement it on the side, where it won't break the existing stuff. And even if you get the vendor to implement it, chances are they are gonna do it the same way IPv6 got implemented initially: By routing it software, so performance is going to absolutely suck. So the first decade after the proposed flag day performance is going to suck until everyone has upgraded their hardware that can do both in hardware.

Next are the random boxes (firewalls or NAT boxes) that will happily mangle all your option bits in the IPv4 header for no reason. Of course while you haven't used any expanded address space everything will seem fine and might even work fine in the lab, but once your flag day arrives and people are supposed to start using it, you will realize it doesn't actually work, because of all those broken boxes in the wild and fun routing bugs and so forth.

And then you get all the regular bugs that come with making any change that were hidden by no one actually using it. You get all the phases IPv6 went through, but much worse and with a couple decades of delay.

The only way to make things work is by using it. The earlier one gets started the better. Wishing really hard does nothing.