You might notice that I never once claimed that the replacement I described would be "easy" or, for that matter, even advisable given the broader real-world constraints involved; just technically feasible in the barest sense. I don't think many people would want to use DOS to design a greenfield system of that kind today, and there's a reason for that. Yes, you can buy newly made "DOS PCs" today, but can you really ensure that today's brand new DOS PC will behave in every way that matters like the actual 30 years old DOS PC that used to control the machinery? That's not a trivial question to answer.

If you design the system from the outset to work with an actual PLC/SCADA or similar (the typical solution for hooking up to big industrial machinery of that sort) that's a bit less likely to come up as an issue, and the hardware will actually be designed for that kind of environment.