I was saying adding a byte to the address so its a 40 bit address which would be two bytes to the header. Obviously it would still have the same issue where hardware and software would be incompatible and would need to be replaced but the same concepts that worked in IPv4 would work in my fake protocol instead of IPv6 where the network needs to be redesigned from the ground up.
How sure are you that 40 bits is a good number of bits? What's your justification? It takes over 30 years to deploy new bits, so you have to be really sure before you start that effort.
40 bits would've bought us a lot of time and would've kicked the can down the road several decades. People from the future would be much better equipped to design a new protocol because they understand their needs better.
How many decades? If several means six, we're already halfway there and at 50% deployment. What's the point of designing something you know will be obsolete the moment it hits 100% deployment?
It really isn't. I mean, at a very basic addressing level, sure, IPv4 addresses and IPv6 addresses are just a sequence of octets. But at a network infrastructure level they are quite different, and IPv6 is (conceptually) designed for large-scale, hands-off deployments. See: SLAAC, NDP, DAD, GUA/ULA/link-local address scopes, unicast vs. multicast vs. anycast, etc.
Also IPv6 addresses are ugly