On the other hand, one could argue that if the dishwasher manufacturer's intention was indeed to prevent user refills, they would have known to already implemen

On the other hand, one could argue that if the dishwasher manufacturer's intention was indeed to prevent user refills, they would have known to already implement their own strict "DRM-style" technological limitations, drawing from the history of printer cartridges. The fact that they haven't may well be a sign of good faith.