I don't know 100% of all the details with priority but I accidentally stumbled upon this not too long ago. I was messing around with Mame 112's features with recording and decided to try making a "shadow" of myself for haphazard training, basically programming all of P2's moves to be the exact same as mine with the directionals being opposite. It looked like priority swapped every match like you're saying but I never took the time to explore and document the frequency. Like Scheiss said, if you want to do that then be my guest. It's likely something I would get to regardless as it's undoubtedly useful in some way or another.
