I have a little background in history. No degree, but a firm academic grasp. I believe there is more to the civilization-choice than meets the eye. What you’re going to read can appease a lot of you people complaining about poor diversity of civilizations.
I believe they started their civ-choice by gathering a lot of academics in history as well as gamedesigners. They gave them a single task: Find the eight most important civilizations of the era 800-1500 that as a whole represent human culture the best. That is a top-down design that I continuously believe they pulled of very well. I am still amazed by their choices. The reason? I believe a lot of the other civilizations that are not in the game yet can be a spin-off of the existing ones. If you ever played command and conquer - kanes wrath, you know what I mean. They took the original three factions and for each faction, they created additional two factions in the expansion. These were specializing on different aspects. In the end, the game had 9 playable factions. The look of them only changed slightly in comparison to the original, but they were sometimes playing completely different.
What does this have to do with the age-franchise? I’ll tell you: You can spin off a whole lot of different empires from the eight existing ones. Take style and feel of the abbasid dynasty. You can spin-off a lot of factions (i.e. persians, turks) from that, even a few african cultures. You can spin off all kinds of southeast-asian factions from the style of the delhi-sultanate. You could (probably somewhat) spin off spain from the HRE. You can spin-off nomadic tribes from the mongols, you can spin-off slavic-nations from the Rus. This means we might still get a lot of civilizations, designed like in AgeII with some units and technologies, just not with their own art or unit-design but as a spin-off to existing ones. I think this is likely to come and also easy to do. I’m looking forward to it.
Again: If you think about the goal of having eight civilizations that are most representative, I keep on being amazed by the choices they made. But to see this clearly takes some insight in the genealogy of history. I implore you to take a closer look!
What they are missing are the byzantines and vikings for their uniqueness. I believe this will come in the expansion. I’m not so sure about the native americans though… But thinking about it: It could be a “challengers” expansion, by the looks of it. The “could be”-empires…