as long as your on pc with construction set you can add them in. just make it a mod.
it could start off with just a big mod of generic normal names from the real world for npc to greet you with.
then do total redialogs for the vanilla games dialog with new voices and maby give some of the characters new sound.
then just leave a space for custom requests, like custom names/quests.
i think it would be very interesting with everybodies desire for more voice acting and could be doable so long as enough people go along with it.
i know i have plenty of time i could devote to it.