> From my experience doing IT in industrial manufacturing, there is a ton of room for them to replace expensive PLCs where they aren't really needed.
From my experience with PLCs, they are hardened and robust to the extreme degree required by the harsh environments in which they are used. Last time I looked, the R Pi was the complete opposite. It can be crashed by just a nearby camera flash, and then leave its SD card corrupt to boot. Fine for hobbyists (apparently). Not fine for industrial applications.