Here are more possible Civ. VI leaders....
Ancient/Classical- Mehmed II
Industrial/Modern/Future- Abdul Hamid II
Industrial/Modern/Future- Darius III
And I have ideas for new Civs....
Ancient/Classical- Bogdan Hmelnitski
Medieval/Renaissance- Petro Doroshenko
Industrial/Modern/Renaissance- Ivan Mazepa
Special Ability- Khmelnytski Uprising: Military units have a +50% combat bonus when defending and a +25% combat bonus when attacking with a non-military unit in the same or an ajacent tile. Non-military units can ONLY defend themselves with a strength of 10.
Cossack Horseman (Same abilities as previous unique unit)
Sich- Replaces Castle, same abilities of a Castle, but grants new military units a random promotion that relates to that unit (land units get land promotions, etc.), and promotions are at random levels.
Industrial/Modern/Future- David Ben-Gurion
Special Ability- Temple on the Mount: Temples provide +50% Gold and +1 Happiness to a city, and have no Gold maintanence. +2 Faith in cities built on hills.
Temple Guard- Replaces Spearmen, retains bonus against mounted units, +100% combat bonus when the Capital has the state religion as the dominant religion. Gains 3 Faith to the empire whenever the Temple Guard defeats a unit from a civilization with a different religion.
Shin Bet HQ- Replaces Police Station, retains Police Station benefits, any spy who detects and eliminates an enemy spy in a city with a Shin Bet HQ gains the empire Gold and Science.
I'll think up more later...
- December 27th, 2013 EDIT
Ancient/Classical- Stephen I
Medieval/Renaissance- Matthias Corvinus
Industrial/Modern/Future- Janos Kadar
Special Ability- Kadarism: All social policies cost 50% less Culture, and each Policy Tree adopted gives 5 Gold per turn.
Hungarian Hussar- Replaces Knight, same abilities, slightly weaker, but can attack twice in one turn.
Freedom Fighter- Replaces Infantry, combat bonus in Rough Terrain and against units with a higher combat strength (+50%). Requires Freedom. If Freedom is not adopted (or no ideology available yet), regular Infantry will be produced.