> Software updates scale _very well_ - once author updates, all users get the latest version. The important part is sysadmin time and config files - _those_ don't scale at all, and someone needs to invest effort in every single system out there.

With IPv6 the router needs to send out RAs. That's it. There's no need to do anything else with IPv6. "Automatic configuration of hosts and routers" was a requirement for IPng:

* https://datatracker.ietf.org/doc/html/rfc1726#section-5.8

When I was with my last ISP I turned IPv6 on my Asus router, it got a IPv6 WAN connection, and a prefix delegation from my ISP, and my devices (including by Brother printer) started getting IPv6 addresses. The Asus had a default-deny firewall and so all incoming IPv6 connections were blocked. I had do to zero configuration on any of the devices (laptops, phones, IoT, etc).

> I upgrade my OS, and suddenly I can use IPv4x addresses... but I don't have to - all my configs are still valid, and if my router is not compatible, all devices still fall back to IPv4-compatible short addresses, but are using IPv4x stack.

So if you cannot connect via >32b addresses you fall back to 32b addresses?

* https://en.wikipedia.org/wiki/Happy_Eyeballs

> I upgrade the home router and suddenly some devices get IPv4x address... but it is all transparent to me - my router's NAT takes care of that if my upstream (ISP) or a client device are not IPv4x-capable.

* https://en.wikipedia.org/wiki/IPv6_rapid_deployment

A French ISP deployed this across their network of four million subscribers in five months (2007-11 to 2008-03).

> There is only one firewall rule set, there is only one monitoring tool, etc... My ACL list on NAS server has mix of IPv4 and IPv4x in the same list...

If an (e.g.) public web server has public address (say) 2.3.4.5 to support legacy IPv4-only devices, but also has 2.3.4.5.6.7.8.9 to support IPv4x devices, how can you have only one firewall rule set?

> So this is a very stark contrast to IPv6 mess, where you have to bring up a whole parallel network, setup a second router config, set up a separate firewall set, make a second parallel set of addresses, basically setup a whole separate network - just to be able to bring up a single IPv6 device.

Having 10.11.12.13 on your PC as well as 10.11.12.13.14.15.16 as per IPv4x is "a second parallel set of addresses".

It is running a whole separate network because your system has the address 10.11.12.13 and 10.11.12.13.14.15.16. You are running dual-stack because you support connection from 32-bit-only un-updated, legacy devices and >32b updated devices. This is no different than having 10.11.12.13 and 2001:db8:dead:beef::10:11:12:13.