Prioritize New Cultures Being Related to or Part of the Histories of Existing Cultures

The Culture Shifting system has many different interpretations, but one of the most compelling is that it's supposed to represent how as opposed to their portrayals in most other historical 4X games, civilizations were dynamic and changed over the course. The prospect of playing as a nation and retracing its path through history over the course of a session if I wished was one of the most attractive things about the system and by extension the game itself. However this isn't possible in the current iteration of the game because nearly all have gaps in their in timelines, so to speak and aren't represented in every era.

To rectify this and to increase the opportunities for RP and emergent narrative gameplay, when adding new cultures, filling these gaps should be prioritized by including cultures that either represent the different dynasties or regimes that ruled their people or geographic area of one of the pre-existing or cultures or another that was ruling that cultures territory at the time. An example of the latter would be adding the Timurids in the Early Modern Era to represent the Persian culture in that Era, because they were ruling over Persia at that time.