Re: how IPv6 address and parameter configuration follows the KISS principle?
"The Router essentially has no Firewall or NAT if using IP6."
Firewalling rules are the same at ipv6 or ipv4. Just make sure you apply them to both, most decent consumer routers will do that for you.
NAT is not a firewall, not even a poor substitute for one.
IPv4 NAT breaks a shitload of things. It's a kludge and a rotten one at best which requires a lot of workaround on IPv4 networks (There is the possibility of NAT in IPv6, but it's 1:1 mapping, not the 1:many of Ipv4 NAT and you'd generally be bonkers to use it unless you absolutely had to)
Anyone raising these arguments as a reason not to go to Ipv6 isn't competent to raise the objection.
Adding "security" and "privacy" was one of the things that badly slowed down initial iterations of IPv6 getting off the ground. If you really want to go and reinvent that wheel then be prepared to spend a decade or two arguing about the minutia, because you're tacking so much onto TCP/IP that you really want to start over and redesign the entire packet structure from scratch - and good luck with getting THAT adopted within the next 30 years.
IPv6 isn't perfect, but it's a hell of a lot better than what we have now - and what we have now is creaking badly. Yes, you could redesign BGP to have more than 65k routes whilst keeping IPv4, but why bother? It'd take 30 years to drive adoption of it when BGPv6 already exists.