I think we have yet to consider potential Civs strictly by the unique art their leaders would bring to the game.
Some considerations when seeing it through that lens:
- A Native American leader in more traditional attire may be more likely than a somewhat westernised one a la Poundmaker.
- A modern leader for Africa may be more likely on account of Mali, Zulu and Kongo using more traditonal attires from their respective cultures. This picture of Menelik is pretty good.
- Still no 16th century European garmants. Portuguese/Italian/Dutch leaders would fit the bill pretty well. All male western leaders in the game are heavily armoured. Need a bit more finesse

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Edit: Another picture. I want to play with him on account of how badass it looks.