I've toyed with the idea of adding new personalities but never could come up with anything terribly interesting. IIRC, I thought of putting in a 'Gates' personality who would start off as a scientist/businessman but who change his strategies so as to become a megalomaniac after he discovered computers.
I think you've got a good point here though. Suppose we have the following victory conditions:
Domination (66% of land and pop)
Conquest (100% of cities)
Diplomatic (everyone is your ally)
Histographic (the default game thingy)
At the beginning of the game, we ask the player to choose his preferred strategy: military or peaceful. This allows us to determine the sort of AI that he will be playing against. With more 'peaceful yet competitive' personalities we may be able to make the peaceful victory conditions more interesting.
Another thing to consider here is the possibility of changing AI personalities as the game progresses. As it stands, the personality is associated with the civ at the beginning of the game and stays that way forever. It's true that the civ's strategic and diplomatic states change, but this doesn't seem to be enough. Frozzy made a good point:
Not only is the specific example he gives rather interesting (we might be able to set it up in such a way that if you really beat up on a nation, they become effectively a vassel; although there could also be factors put in so that they tend to move towards independence unless you assimulate or pacify them or something) but also this idea of changing personalities might be able to give us a better way of dealing with a human player's changing strategies.AI leaders are booted every so often and they have civ-like traits. So, the French AI could have Joan D'Arc as a leader (militaristic), and then be booted out and Daladier put in if France lose a war (he would be peaceful). This would decide the way the AI relates to you