I've discovered that I've got a lot of new thoughts or questions about new leaders. I know that currently you're busy with other aspects of the mod but I just have time now so I'll post it now but feel free to answer later when you'll have free time. Oh, BTW, don't type the answer in Safari. Type it elsewhere and copy-paste here.
Celts
Llywelyn of Wales would be a good addition. The only problem I see is that 4 of 5 leaders would represent Insular Celts. I'm not sure if this is good.
England
With Alfred of Wessex added, all the main periods of English history would be represented.
Netherlands
Do the Netherlands represent the whole Benelux? If yes, Leopold II of Belgium can be added.
France
Well, I've found more arguments for replacing Richelieu with Karolus:
1) There is a big gap between Clovis and Richelieu, and a too small between Richelieu and Louis (they were even alive at the same time!). There are better gaps between Clovis and Karolus, Karolus and Richelieu.
2) IMO, every culture/state should be represented with one civ. For example, even though the Celts are the ancestors of the English and the French, they are represented only by Celts. The Franks should be represented only by one civ and I think it should be France.
3) There are 2 other good leaders for Germany which can be both added if Karolus is removed.
Germany
If you remove Karolus, both Barbarossa and Hitler can be added. Then Germany would be represented by Barbarossa, Maximilian, Frederick, Bismarck, Hitler. Sounds good enough for me.
Scandinavia
I don't know. This civ represents several states with a rather long history. Maybe a 4th leader can be added.
Poland
I think 4 leaders can be afforded. Casimir, Vytautas, Sobieski, Pilsudski sounds good for me.
Russia
An ideal combination would be Yaroslav, representing Kiev, Alexander, representing Novgorod, Ivan, representing the Duchy and Tsardom, Peter, representing the Empire (Yekaterina would fill the gap better but Peter is far more important), Stalin, representing the USSR. I'd really love to see the Principality of Polotsk represented (by Vseslav) but I'm probably biased.
Hungary
I think three leaders is good enough.
Greece
A 5th leader from the Hellinistic period would be good.
Rome
Are Romans and Italians the same people? If yes, I'm happy for them to stay as one civ. About leaders, 3 leaders should be Roman and 2 Italian. I'm happy with the Italian ones but it may be more beautiful for the 3 Roman leaders to represent the Kingdom, the Republic and the Empire, although adding a Kingdom leader just for the sake of it doesn't seem right. Having both Julius and Augustus also bothers me but they're representing different states, so that's OK for me.
Byzantium
Three leaders are probably enough for Byzantium.
Phoenicia
The only other possible leader I can see is a Phoenician leader representing another city-state (not Sur).
Spain
You've said (written) that colonial countries are covered by their "parent" civilization but it was never represented with leaders. Spain is a perfect example to show it because there are plenty of worthy Latin American leaders. Just pick one of them.
Portugal
Maria would be a great 4th leader.
Egypt
Three leaders is definitely enough and they are probably the greatest of the Egyptian history.
Nubia
Three leaders (with Merkurios) would be OK.
Ethiopia
Four leaders is a good amount for an African civ.
Berbers
I think they deserve more leaders. You can add a leader of Numidia or Garamantes, maybe both.
Mali
I'm glad with the current four leaders.
Kongo
Two leaders, one representing the kingdom and one its vassals, are good.
Swahili
What does this civ represent? Only the city-states or something else?
Zulu
What does this cov represent? A period of 81 years during 10 of which it wasn't even independent?
Sumer
Two leaders are OK.
Amurru
Unless you want to represent another city-statrle, three leaders are enough.
Assyria
Three leaders are (more than) enough.
Hatti
The Hittite Kingdom's vassals and related allies, and the Neo-Hittite city-states of Syria aren't represented. It may be good to represent them.
Israel
I'm really not sure. Maybe a modern leader is needed, maybe not.
Arabia
The five current leaders please me both historically and geographically.
Persia
I'm absolutely sure that unfortunately both Achaemenid leaders can't stay. A Median leader (Cyaxares, for example) can be added. What concerns the 5th leader, either a Parthian or a more modern one.
Kushan
Covering only one empire isn't very good. Does it have continuity with some other states?
Turks
I'm really confused now what they represent.
Mongolia
What is Mongolia representing?
Tibet
Two leaders are probably enough..
India
India absolutely needs a 5th leader, either a Pala emperor or Shivaji Bhosle.
Tamil
A third, Vijayanagara leader would be a good addition.
Siam
After the addition of Naresuan, the three main kingdoms of Siam would be represented.
Angkor
Currently, both leaders represent the Khmer Empire. What else does this civ represent?
Vietnam
Three leaders are enough and are from different historical periods.
Indonesia
The Muslim states and the Malay still aren't represented. I'm not sure whether a 4th leader is needed.
China
China deserves a 5th leader. Probably the best cchoice is a Han.
Korea
Three leaders are good.
Japan
I'd like to see a Kamakura leader.
Polynesia
As the only civ in its region, representing a lot of different islands, I think a 4th leader, representing Tahiti or Rapanui, can be added.
America
Three leaders are enough. We have three leaders representing the three centuries of the existence of the USA (the 21st is too recent). So, in the following 40 years or so, America would be good with the current leaders.
Iroquois
Two leaders are good
Sioux
The only thing that bothers me is the fact that both leaders are Lakota and Eastern Dakota and Western David's aren't represented.
Anasazi
Where have you found information about Kochininako?
Aztec
I'm OK with two leaders but Montezuma should be replaced with the most important tlatoani, but I'm really not a specialist.
Maya
A third leader is acceptable.
Inca
I'm not sure if they have enough connection with the Wari.
Brazil
I'm not sure that a third leader is needed.