The issue is that it's impossible to make anything with more address space directly interoperable with IPv4 since it has a fixed 32-bit address space. Unless yo

The issue is that it's impossible to make anything with more address space directly interoperable with IPv4 since it has a fixed 32-bit address space. Unless you consider NAT from your extended IPv4 towards IPv4 interoperable in which case IPv6 is already interoperable with IPv4 (since there is NAT64 among lots of other schemes). However you will always run into the exact same issues we are facing with IPv6 today.