> IPv4-with-more-bytes is not backwards compatible with IPv4

Neither is IPv6

> To get, basically, the same effect as moving to IPv6

The only thing that IPv6 solves which is of interest to 99.99% of the users is having more adressable space. The rest of IPv6 features are either things that nobody asked for, or things which are genuinely worst compared to IPv4.

I consider the mere fact of enabling IPv6 an unacceptable security risk, as I would now have to make sure my IPv4 and IPv6 firewall stack are perfectly mirroring each other. That would be trivial with IPv4-with-more-bytes, it's a nightmare with IPv6.

Do NAT64 and just worry about IPv6 if not wanting dual stack.

All of IPv6 features are just direct effects of having more space and not. Basically IPv6 "features" is just getting rid of IPv4 workarounds.