You'd still need to update and replace every system a packet would touch. Why just add another 8 or 16 bits and make it where we'd have to go through this entire painful process again? IPv6's design was "we never want to do this again".
An example of this "we never want to do this again" is only 1/8 of the v6 address space is currently marked usable for allocation. We have 7 more chances to change allocation methods without having to update or change any system.
Not to mention that we can “visualize” the segments and networks by the numbers. Makes it easier to recognize, as an analogy,
This state, that city, this road, that house.
Versus ipv6. Of course there’s so much space in v6 that it isn’t an issue except it’s such a pain to work with for people who tend to think in ipv4 octets and bit masks
IPv6 is also built like that and IP4 never was globally (except the country/region part), but it could be continued to be that router in the building, that device that network card in the device and even give separate IPs per service and serve them all on the same port.
There's way more to ipv6 than additional octets. I don't run ipv6 on my wlan (pretty much only for my mobile phone) because I can't be arsed to wrap my head around ipv6 autoconfig and NAT (or rather not NAT) whereas setting up dhcp is a breeze.
It really isn't, but vendors often make the IPv6 config optional and often don't have an auto-config wizard for IPv6 like they often do for IPv4.
Take Ubiquiti EdgeOS, setting up a PPPoE with IPv4 has a dedicated GUI wizard that shows up when you first log on, but IPv6 config is all confusing CLI commands.