IPv4-with-more-bytes is not backwards compatible with IPv4. So you'd have to replace/upgrade every existing network stack, both hardware and software. To get, basically, the same effect as moving to IPv6.
There were backwards-compatible protocols proposed, such as EIP, but the committee chose a backwards-incompatible protocol for v6. Their assumption was that v4 would run out of space in a single-digit number of years and everyone would be forced to migrate. The past 30 years have shown that not to be the case.
> 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.