However many we end up getting I think there should be an option to play a huge earth with all nations historically placed. That would include all expansion nations as and when they are released.
Trying to eek an empire out of an Earth game with 40 or 50 civs jockeying for position would be awesome. Might need to tweek the rules, timeframe or whatever to fit it all in of course.
That's exactly what I wanted as well, a giant RFC version of Civ, it would be awesome! The only scenario I usually play is RFC and it is my favorite one, Civ V should have that scenario or option.