Those are probably the two most requested nations but I haven't seen anything official and I wouldn't wager on ever getting a playable nation that's already available as a coalition. It doesn't make sense to have them both places.
They should totally add Nigeria. With all the Nigerian internet scams, taking suckers for their money, I think that, along with the the Embassy, Nigeria would be a great addition.
I remember Tim Train or one of the Developers did mention that appearing in coalitions does not mean that the nation disqualifies for a new nation. I think that was the time when coalitions first came out. Hoping to see America and Russia as new nations in atomic age. It would be funny to call it "atomic" when none of the major powers with nuclear arms are in it. America being an air power offering bonuses to planes, Russia offering bonus to factory troops, maybe Gatling gunners or commandos? This will bring more diversity to game play.