

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.
At this point, I’ve seen far more people being almost violently anti-rust than I’ve seen people being weirdly enthusiastic about rust. If Rust people are Jehovah’s Witnesses, then a lot of the anti-Rust people are ISIS.