I went trough some civilization and leaders from Call to Power (which was for those not familiar kind a offshoot of Sid Meyer's Civilization for a while) and found out interesting leaders and civilizations that some latter civs actually used it.
One is specially interesting: Barbarians lead by Attila
This might actually be the last leader in NFP? (but that's for another thread)
others:
Cuban, Hebrew, Mexican, Nicaraguan, Nigerian, Thai, Welsh...
They introduced Assyrian, Polynesian and Indonesian before any "official" Civ game. So in this list might be some future new civilization for dlc in 6 or for 7.
Also, if they count Civilization 4: Colonization there is few more civs and leaders that could count as old:
Mangas Coloradas of Apache, Agueybana of Arawak, Oconostota of Cherokees, Cunhanbebe of Tupi, Simon Bolivar was already there, Samuel de Champlain etc. (btw: I liked civ4col a lot)
Conclusion: there is more option, more.. give us more
