While I agree with your premise for internal networking you fail to understand what the parent was referring to with 4.2.2.1 or in my case 4.2.2.2 and a bunch of other Internet addresses that are commonly used during the diagnostic process. Remembering an internal subnet is easy, nevermind the fact that I run about 20 VLANs with different subnets on each one. My whole topology changes when I switch to IPv6. Expect a lot of resistance to this change when it affects everything on your network at a fundamental level.
To most of us, the idea of subnetting internal addresses spaces makes a lot of sense as it is an easy way to control who has access to what at a layer 3 level. With IPv6 and a single subnet, you now have to rely on Intranet based gigabit firewalls to keep everything locked down. In my network, you're on your VLAN and if you change your subnet to try to gain access to a server you won't get anywhere. This is besides the fact that only the newest layer 3 switches even support IPv6 routing. Many many businesses run switching and routing gear until it dies and the vast majority of it doesn't support IPv6. On top of that, most even brand new printers don't come with IPv6 support and all my security cameras are in the same boat. Yes you can run IPv4 tunnels but that means you have to maintain both IPv6 and IPv4 infrastructures until everything catches up. There is no smooth transition to IPv6 for any company of size. Tiny shops can get by probably pretty easily as they don't have lots of bandwidth considerations. My load balancers and firewalls also don't support IPv6 and they are less than two years old. I will grant that there is a firmware version I can install for the firewall to get IPv6 but the balancer is screwed.
Bottom line, expect a lot of resistance to this change as it is the biggest change since going from token ring to Ethernet. Combined with the fact that many people were taught IPv4 in networking classes and have had no exposure at all to IPv6 you get a whole lot of experienced professionals that now feel like noobs.
Change can be good, but right now NAT works fine for the majority of us so there is no compelling reason to change to IPv6.