Re: 30 second ipv4 redesign?
Network kit relies on the address info being x bytes into the packet, if you want to backward compatible you need to keep the IP packet header size constant and signal that an alternate or additional address is somewhere else. Just fiddling with the number of octets will just break what is already implemented.
There are largely unused options in the IPv4 header already that could be re purposed to indicate to look for the IPv6 address somewhere else but then that breaks encryption and other mechanisms reliant on the integrity of the packet.
you'd need to assign an IP specific for IPv4 to IPv6, maybe near the multicast range like 18.104.22.168 and then amend the protocol IPv4 field choosing a new value to reflect IPv4 to IPv6 and then in the option field you could then put the real IPv6 address. Routers in the ISP could then NAT IPv4 to IPv6 rewriting the headers. It will likely break any security like VPN's, TLS and provide a nice attack vector that most sane techs would want to steer clear off, but that's the route i would go to transition from 4 to 6 or beyond.
The main problem is that the new addressing scheme needs to be transparent to the old IPv4 kit which often did as much as possible in hardware to be quick and cheap, and also who owns and runs (ISP, IANA, Google, MS, Amazon) the special IPv4 address that DNS suddenly needs to respond with to keep legacy kit happy. Also doing things in software is a lot more cpu expensive than in hardware, which will slow lower powered gear no end and cause resourcing/capacity problems for service providers.
People need to also bear in mind that Layer 3 addressing is mandatory when going from 1 network to another, we still autonomously use MAC addressing at Layer 2 connecting with hosts on the same (v)LAN using arp to obtain the MAC of the machine to forward our info to adding it to the destination Ethernet frame.