Because that's basically what v6 did. It just added enough octets that we don't need to turn around and do it again immediately afterwards, since deploying new L3 protocols is hard enough as it is without needing to do it twice.

That doesn't solve the fundamental problem of IPv6 adoption: _all_ equipment along a network path needs to be updated to be compatible with the new addresses for them to be usable.

Yeah, and if we're going to be changing all of the equipment, why not take the time to smooth over some of the other known warts besides address space?

It's my understanding that IPv6 is essentially that, and not just a move to a 128-bit address space

This means changing every piece of network equipment everywhere.

And if you need to change it, why keep all the broken parts of ipv4, if you can fix them (atleast partially), like we did in ipv6?