> Then it would be possible to reuse old embedded equipment.

Unlikely, virtualization/emulation has been a thing well before this project and you can just buy USB to RS232 adapters. There are GPIO solutions for industrial PCs other than the parallel port. Or you can simply buy new industrial PCs which have those ports.

If you find an industrial appliance controlled by genuine old PC hardware that hasn't been replaced, the RS232 ports are the least of your concerns.

In my experience, such machines usually have something insanely proprietary plugging into a custom ISA card, and whatever is connected to it usually doesn't take too kindly if the bus timings are off. And neither does the accompanying bare metal software that relies heavily on timing loops and hardware peculiarities.