Having worked on for a short stint with some power plant control systems, I can say that, at least the systems I worked with, were quite niche. The actual control was happening on these racks that ran a VxWorks OS on some Motorola, I think they were, MCU's. Despite this, the systems were interfaced with some Windows machines that did supervision. When they were operating, they had redundancies, and were quite locked down. Of course, at that time, I was a noob and did not understand _everything_ that was going on in there.

Actually, now that I think of it, the WDPF system it was derivated off was used in some nuclear power plants as well.

Regardless, what I wanted to say was... being obscure, while it makes things mildly harder for skiddies is not a big deal for state actors or more resourceful attackers. The Stuxnet was highly targeted and they got access to specific vulnerabilities in the Siemens DCS systems that were running there. Just having exotic systems is no guarantee. I agree, obscurity is a layer of defense in depth, but no guarantee. Surely you don't suggest they use a new purpose built HW for each control system design. Also, control systems DO need to have their SW updated as well. It's obvious you can't make it hard read only. You do have physical lockout mechanisms for this though.

Not to the point of detonating them - they have a lot of physical safeguards.