A PLC and a Arduino share the same problem - to make changes you need to attach a cable and use an external device to edit/change/upload a new program. Not only that, much of the software needed to do this is not non-geek user friendly.
Now you could take an Arduino Mega, add an ethernet/SDcard shield and add another display/menu button shield - but by that price point you could have bought 2 PLC units. Now if you go and draft a group from the EE program they could breadboard an Arduino circuit, add all the required sub circuits then once this is tested - design a single PCB that is ready to interface with the air solenoids and sensors and send that design to a PCB fab ( maybe in China, {don't shoot the messenger} ) and get back a batch of ready to use boards.
It all depends on what your stated goals are. I would want to have a near turnkey kit that could be sold to Master Caster owners that would be a simple bolt on as much as practical. Maybe offer a clamp on drill guide for locations that users need to modify the chassis etc. on a refundable deposit basis.