Well, I know some mods have a feature that allows barb cities to eventually evolve into new civilizations (randomly becoming one of the civs included in the mod). That may be a feature of RevDCM, which is basically a mod component used by many mods, but I'm not certain on that. Pretty sure that Legends of Revolution, Caveman2Cosmos, and ROME(AND) have this feature, but I think some others do to.
Also, Rhys and Fall of Civilization (RFC) is a popular mod that spawns civs historically in the game relative to the approximate historical date and location. So you start a normal game with like Egypt, China, India, Babylon (or Sumer) on the map, if you play one of those civs. Greece and Rome spawn a bit later. France spawns around 700AD or thereabouts. (If you start as a later civ, the game auto-plays X amount of turn until the civilization would normally appear in the game)