The one thing you can't do with IPv6 is yell the address across the room to the technician plugged into the switch trying to ping the node.

This is equipment that uses all statically addressed devices. And ignoring the fact that IPv6 is simply unsupported on most of them, there are duplicate machines that share programs. Regardless of IP version you need NAT anyway if you want to be able to reach each of the duplicates from the plant network.

Good luck trying to find industrial stuff that supports IPv6, hell most of it is still serial.

I have legit heard that serial is security mechanism because it cannot communicate long distance like ethernet.

Of course you can do IPv6 magic that hides IPv6 from the end device, but nobody understands how that magic works.