Now it comes from a computer model, so there could be errors or exceptions— I'm thinking extant uncontacted peoples, here. The model accounted for this possibility, as the paper notes: ...in order for a remote island to affect the MRCA date, it must have been colonized prior to the lineage of the mainland MRCA reaching the source population and it must have remained genetically isolated until very re- cently in order for there to be surviving people with no modern mainland ancestry.
Remember that uncontacted peoples are uncontacted by us; the ones we know of have regular if infrequent contact with other tribes, so if contacted tribes share the MRCA it's quite probable that uncontacted ones do as well. Could there be a cache of 50-100 human beings somewhere on this planet who happen to share an MRCA with us who is older than the one shared by all other living persons, maybe 10,000 years? Sure. But they would be the only ones out of 7 billion.
The place this really falls down would probably be extremely isolated tribes which have had little if any external contact - there's very few nowadays, but some are remote enough that no pairing has probably happened.
Of course Genghis Khan was unusually prolific, and the direct patrilineal aspect is what makes it special, but you don't have to go far back in time to find an ancestor you share with one in ten people, let alone one in a hundred.