All they would have to do to make pops make sense in Rome 2, a Dark Ages game, CK, EU, HoI, and EvW (Assumingly a sequel) would be to make the pops before Victoria 2 more accepting of their ruler and more willing to immigrate (dynamic movement of populations from a European nation to a Middle Eastern Crusader state and from a European nation to an American colony would be incredible) and the after Victoria 2 have them less willing to immigrate (except for huge events, like tsunamis, famines, etc.).
And it would also make internal politics make more sense so that CK and EU can stop relying on internal events. It could also be used to make HoI and EvW more dynamic with revolutions, new regimes put in place, the decolonization of Africa, and the eventual fall of the Soviet Union as their people become more and more inclined to a democracy.