Hello, I just recently discovered your mod and it is great. I like that you are equating civs with cultures and not just including as many civs as possible (I do not want to be playing a game with Canada in the ancient era). After exploring your mod a bit, I do have some feedback on the civs.
Should America be in the game as they are just a colony that broke off from England? The same with Brazil as they were a colony that broke off from Portugal.
I do not think the Byzantines should be a civ under your criteria. The term Byzantine is an anachronism. The "Byzantines" called themselves Romans and the Byzantine Empire was just the surviving eastern half of the Roman Empire. I would add some of the Byzantine leaders to the Romans and get rid of the Italian rulers for the Romans. Maybe add the hippodrome to the Romans.
I think it's time to bring up again my view on how the Americas can work well in the logic of Xyth and his mod.
If America or Brazil are just a colony of their mother cultures, then they are an offshot, or a phase, in the mother culture's historical span.
With the dynamic city naming mechanism, it should work perfectly.
Exactly as great Kiev or Novgorod are different geographical phases of Russian history. And just as a Baghdadi Abbasid regime is a phase of the Arab history.
The English empire ruled America anyway, it's just a matter of shifting the centre to there.
I would argue that the difference between a Shiite Persian dynasty and ancient Persia is harder to bridge than the difference between the Kingdom of England and the United States of America.
I mean, America and Brazil are centred around cities that the mother cultures built, and consist of a population from the mother cultures. It's not a complete conquest.
Moreover, I would include colonial governors who were not fully soverign. John Wintrop and Fontenac, or any other worthy viceroy.
Spain should be an fascinating Civ in this sense, having its cities alternating to those of Gran Colombia, Mexico or Argentina, depending on the leader.
Now the real question is what do you do with Hellenistic leaders - Menander, Nikator, etc.
These were some fascinating cultures which you can not overlook, kind of like America and Brazil. The main difference is that the Hellenists were plain conquerors - ruling mostly older cities, and ruling over a population of previously existing cultures.
So I guess they don't fit here as much as colonial leaders do.
In my mod I plan to create them as a fluid "hellenistic" civilisation, but in the logic of History Rewritten, the best they should be is a wild form of Greek leaders.
And did anybody say Crusader states?
As for your suggestion to remove Italian leaders - I don't see why Italians should be different from other post-Roman civilisations, such as Spain for example. Several hundrends of years after the collapse of the Roman world, many new cultures emerged on these grounds, with the aid of some Latinised-Germanic overlords. Those were West Francia, Visigothic Spain, the fragile Kingdom of Italy, and the Sardinian Judgedoms. All four are equal in their "claim" to be a civilisation, in my opinion. I'll go as far as saying that all four are
almost equal in their "claim" to be additional leaders under the Roman civilisation. Which I am against, of course.
Anyway, having Eastern Roman leaders within the Roman civilisation makes sense.