@p >It's just IPv4 but we've changed the size of the address space to either 64 or 128 bits
That would break compatibility with everything entirely and would require making modifications to every single IPv4 device.

Every single "solution" to the IPv4 address exhaustion problem I've read either would lead to things being more broken than before, or would be way more complicated and burdensome to implement than just leaving IPv6 enabled.

>Maybe someone *is* doing it.
Why would anyone be wasting their time implementing brokenness when IPv6 is the solution?