Way late to this but actually had a discussion with Professor Koons during office hours today about this subject. He works at my school. He seemed to think it would serve as a presupposition even in the cases in question. He also agreed with Pruss’s related argument through objective probabilities.
Lucky guy. Pruss has a paper on his website on probability and the PSR where he expands the argument.
Camoden, any way you could elaborate on what he said? That's cool you get to interact with Koons in person, he's definitely one of my favorite contemporary philosophers.