I believe that you could get significant cost savings by designing your own MCU board
No doubt he can get some significant hardware cost savings, but what about support.

We have not heard anything about how 'standard' the application is and that should be the significant decision factor.

One thing that is almost always overlooked in the excitement of starting a new design idea is the impact on support.

If the end user currently modify the PLC code using ladder logic, I guarantee that a replacement product programmed by other means will result in all reprogramming becoming a support call.

What good does it do that you save hardware cost if the result is that you must hire (additional) support people.

The end user intertia is total. You, as a designer, see it as exciting to learn new stuff, the end user see it as a chore (s)he is not willing to undertake.

So: do not overlook the impact of 'saving', you may score a point and lose the game.

Please DO understand that I am by no means a lover of PLCs, just a realist.

Erik