I just wanted to make an addendum here, since I was reminded of this topic by your other topic.
The uniqueness of the factions is going SKY HIGH compared to what I was thinking. Here are the bullet points distilled down (I'm short on time):
1. The story behind this game is being adjusted so that the race that is landing has one human -- you -- with them. In the case of multiplayer, which is co-op only, then of course it's one human per race that is landing.
2. You-the-human are basically cooperating side by side with the racial leader that you select for your faction at the start of the game. So it's a partnership between the human and the racial leader.
3. The cities that the human-co-led factions are building are all using the same general tileset, and they are fairly human-inspired. The tileset is huge, and varying those between races would just make the game impossible to understand, we feel. Aside from the art costs, of course.
4. When races are already on the planet -- aka, controlled by the AI -- then they have no human influence on them, and are much more entrenched. They have completely unique building tilesets for each race there, and the tilesets are STRANGE. Previously it was just going to be tilesets for the 6 races you never play, but now it's for all 14. Each race (in the hands of the AI) has its own rules for how it builds and so on. They are extremely unique from one another and from you.
5. AI-controlled races also have "underground buildings" that you can detect via sonar, but not directly see. These can form kind of an underbelly under the part of the city that you can see. So this basically lends a form of uncertainty/fog-of-war that is implicit, because what you see on the surface is not guaranteed to be all there is. Sometimes certain key buildings like power generation and so forth will be hidden away underground or underwater. Bring your remote sonar crews to find out!
6. There is a "social progress" screen that is kid of vaguely like the Culture screen in Civ 5, and there are 9 categories on there. 8 of which are actually rewards, and the 9th of which is progress toward a social victory condition. Only human-controlled races use Social Progress at all. Out of those first 8 categories in which you can gain your social levels, 1 per human-controllable race is swapped out each time.e So if you play as the Skylaxians, for instance, you'll lose the social category of Climatology, but you'll instead gain Skylaxian Lexicon.
7. Out of the 8 races that you can play as, there are some special rules that apply only to them when they are in your hands. Really the way the AI uses... everything... is completely different from how you use anything. Two different games. Or really, 15 different games, I guess. Anyway: when the races are in your hands, depending on which you pick, the special rules and bonuses can make things implicitly harder or easier to manage. The Krolin, Skylaxians, and Zenith are considered Standard complexity. The Burlusts, Evucks, and Fenyn are considered Hard. The Boarines and the Peltians are considered Very Hard. Note that this is independent of actual difficulty level, and instead refers more to how complex that race is to play, and how hard it is to win with that race on a given difficulty level. So if you are disappointed that your favorite race is not "hard enough" or is "too hard," then you can always just adjust the main difficulty to make the overall scenario harder or easier as appropriate. For your first playthrough, it's advised that you go with one of the ones that is more standard complexity, though.
8. Various technologies get replaced depending on which you are playing as. Additionally, various diplomatic options appear, disappear, or get replaced depending on which race you are negotiating with (so that's one that varies only when the AI is controlling them, since you can't do inter-player diplomacy since it's co-op).
There is other stuff as well, but that's enough for now.
About BalanceThe most immediate question is "how do you balance a game like this?" The most clear answer is "you don't." In the same sense that AI War is not balanced between all its scenarios, neither will this be. With AI War, depending on what you select in the lobby, you may have an easier game or an insane game. It's like fine-tuning your difficulty. Turn on the Zenith Trader, and that's a nice little boost for you for the most part. Turn on the Human Colonies, and that's a nice little penalty.
So when talking about the game from the standpoint of what options you start with, it's not meant to be balanced. If you get really good with the Burlusts and can win on difficulty X with them easily, but have trouble with that same difficulty with other races, the game is not broken or unbalanced. That just means that for the particular scenario you are working with, you need to crank up the difficulty for the Burlusts. There's a good chance someone else is going to have a harder time with the Burlusts than you do, anyway. I can hardly play Age of Empires III with any faction other than the French, for instance; and I know they are not the most powerful.
When it comes to the lobby options, the idea is the same as with AI War: let the player customize, and come up with scenarios that are easier or harder on lots of vectors. Whatever the case, you're going to have an interesting game either way unless you're just really playing way below your skill level for some odd reason.
To the larger question of balancing things ONCE you are in the game, the answer to that is basically the same as with AI War: it takes a while (like Starcraft), and is an iterative process. And having differentiation between the races in the hands of the AI doesn't affect that at all, because they are meant to vary in difficulty. Same as with dealing with different planets in AI War. So it's really down to balancing your own options and making sure that there are none that are completely useless, and none that you use exclusively.
If this sounds a lot like AI War (partly because I keep comparing it), then that's because it's rather the same philosophy.