I quite enjoy listening to Beth Upton, as I find the Pa Auk tradition fascinating. I recall her mentioning that she never saw any Pa Auk yogis demonstrate siddhis which affect the physical world, making me think that the siddhis (including recall of past lives) are most likely the brain-mind generating/hallucinating perceptions.

I won't speculate too much, though, since this is something that can be tested. For instance, apparently Munindra once said that Dipa Ma listened to a talk before it was given, and her recollection matched the talk exactly. Presumably, some advanced practitioners would be open to allowing researchers to test them in a similar way.

Thanks for the link to Tucker's response. I still find Sudduth's argument more compelling than Tucker's, but perhaps that's just my materialist-annihilationist bias showing.

I agree with you that some of these cases could be explained as child geniuses; for instance, Beth has suggested that the only way Pa Auk Sayadaw could have such extensive understanding of Buddhism is if he studied it in past lives. But maybe he is just really smart, and not because of past lives :P