Hard to say. Firaxis have said this will be the game with the most leaders (including personas) but some people think they forgot that Civ4 launched with 26. So five personas (from the higher priced editions + one of the Napoleons), ten leaders with a first look, Amina, Himiko, Ben Franklin, and Napoleon means we're already at 19. The ESRB revealed that Frederick and Catherine the Greats may be in the game, and people expect a Hawaiian or Indonesian leader to round out the exploration reveals. Are there another five leaders on top of that? Firaxis' lips are sealed but I suspect maybe not.
On top of that, they've been revealing one leader per week and there's only 11 more Thursdays left until the early release, with one of those being Boxing Day, so there simply may not be enough time to reveal 12 more leaders, unless they just break the scheduling of course.
Thanks. Taking all that into account, could this look like a plausible roster for the remaining leader reveals:
Confirmed:
Amina [Songhai]
Benjamin Franklin [America]
Himiko [Meiji Japan]
Napoleon (two personas) [France]
Speculated based on ESRB:
Catherine the Great [Russia]
Frederick the Great [Prussia]
Additional:
Polynesian leader (Lili'uokalani or Kamehameha) [Hawaii]
Victoria [Britain]
1x new, curveball leader along the lines of Machiavelli. Possibly a Mexican leader [I posted a separate thread on Frida Kahlo as a potential curveball], or a cultural leader not linked to any of the launch civs.
1x series favourite, revealed as a standalone or alongside a civ with a tenuous connection: Genghis Khan (alongside Qing?), Gandhi (alongside Mughals?) or Shaka (alongside Buganda?).
Personally I think that Frederick the Great might not be in at launch, because I think Prussia/Germany is going to be in Right to Rule DLC. I have a feeling that that the ESRB leak might have been based on both the game at launch and the already announced DLC. I could be completely mistaken.