Another day, another Godwin's law of networking.

>It was doomed the moment you had to maintain two separate stacks

Pray, tell me, how are we supposed to extend IPv4 with another {insert a number here} bits without creating a new protocol (that neccessitates running two stacks)?

Suppose that you have an old computer that understands only 32 bit addresses -- good ol' IPv4. Let's name it 192.168.10.10.

It then receives a packet from another computer with hypothetical "IPv4+" support, 172.12.10.98.12.4.24.31... ...Wait a minute, it can't, because your old computer understands only 32 bit addresses!

What if we really forced it to receive the packet anyway? It will see that the packet is from 172.12.10.98, because once again, it understands 32 bit addresses only.

It then sends back the reply to... you guessed it, 172.12.10.98. Not 172.12.10.98.12.4.24.31.

Yeah,172.12.10.98.12.4.24.31 will never get its reply back.

Do you see why any "IPv4 with extra octets" proposal are doomed to begin with now?

It wouldn't be able to receive it. That simple. Which is not a problem, any server would still have an old ipv4 address (172.12.10.98 from your example), like they currently do and probably will for decades.