The issue is really forwards compatibility. Every ipv4 address should've been kept valid in all ipv6 networks. Step 1 would've been to leave all the routing, D

The issue is really forwards compatibility. Every ipv4 address should've been kept valid in all ipv6 networks. Step 1 would've been to leave all the routing, DNS, NAT, DHCP etc as-is and just get people's devices speaking ipv6. And we would've already been there years ago. Once that's done, DNS and DHCP can be updated, then people can start using the extended address space by splitting up their blocks. So if you previously had 1.2.3.4, you now also have 1.2.3.4.1 etc. It's actually not too late to do this with the existing v6 header.