As many allready has mentioned, I too, want to see Civil Wars, "new nations" that comes form revolution etc. You might want to repell (spelling) the revolt, or accept it and gain possitive diplomatic points.
Could be in a way that the Vikings could be Norway, Sweden, Denmark etc. Norway could then be divided into Iceland perhaps. And so furth. Perhaps it could be so that the "city names" had stats like "culture, people; norwegian, swedes, danes" Or a specific region could revolt... Anyway I good idea that some has come up with here.
I also want to see total capitulation. That I have overrun 70% of a civs cities, and would no doubt also run over the rest, that the civ could capitulate, living me all their cities. If an allied of that civ captured one of these cities however, that city becomes the original owner againt if you know what I mean.
So say in a WWII scenario, Germany has captured France. But US forces liberated Paris and suddenly the French is in the game agian...
Also, allies should be able to move troops, into the same tiles, move ships into eachothers cities. So that if a civ is struggling, an allied could send some troops in to defend that civ. And also, as someone else has mentionen give or sell units to eachother.
Propably mentionen lots of times before; Air-units beeing able to sink ships, kill land units. Sea-units beeing able to kill landunits with bombardment, able to shoot down airplanes (rarely that would happen I guess)
More peoples than civs... If you know what I ment, that not all people have their own civilization, they are just parts of one major civ. Beeing able to name the Barbarian tripes when you put them out on the map (in editor) And as other have said, let them have more meaning that today, kind of like a mini civ (and when a major civ is beeing killed, perhaps that mini civ could take their place?)
Without aqueducts it was only time before your marketplace would go up in flames!
