Choosing civs to fill the world map is the worst way to choose civs.
Have to disagree there. Different regions bring vastly different cultures and adaptations to different environments that only serve to increase the variety in the game's aesthetics and play-styles, respectively.
That's not to say it should be ones only criterion, but I'd rather have an expansion with nine civs from all over the world than nine civs from Europe and the Middle East, even though Firaxis would have no problem finding nine perfectly qualified civilisations from just those regions.