I actually had bishops in mind more precisely, as such a list would often look quite different from its contemporary list of popular noble names. Anyway I dont think there are that many available sources for truely lowborn people when it comes to naming patterns (a bit more towards the end of the game's timeframe but I hardly think it would be consistent from culture to culture to be exploitable).Sure but remember that lowborns in the game are hardly real lowborns. It would make no sense that the game was throwing commoner knights at you. It's clear they're mostly representing the lowest strata of the nobility.
Lock by date is something the game needs desperately, for heraldry, for naming, for clothing...
But yes not peasants per se, but a mix of lower nobility and actual people of low birth. If the weight are additionnals like they are for their emblems system then all you have to do is to throw a few actual historical bishops names into the mix to make it a bit less redundant with the generic list (reasonnable enough to implement and optionnal enough to not change anything if/when not used). I'm not sure the dynastic weight system is enough in that regard but I'll admit it's also not as critical as having the possibility to tailor different lists for each starting dates.