First post of a long-time lurker.

I think, after reading the thread, that at least some of the slots should go like this (Disclaimer, I know that the EB team prefers to refer to factions as they referred to themselves, and I do not know how some of the below referred to themselves):

1-Kyrene
To stop the Carthaginian-Ptolemaic desert wars.

2-An Illyrian tribe, perhaps the Ardiaei?
Organised under Queen Teuta, the Illyrians were only subjugated by Rome after forty years and two wars.

3-A Numidian tribe, Massyli or Massaesyli
To stop complete Carthaginian domination of northwest Africa

4-Attalid Kingdom
Ruled Pergamon and Phrygia until giving it to the Romans. Fought off the Galatians.

5-Taxilan Satrapy/Gondhara
To prevent the "Big Blue Monster of Baktria", and because you can't have India without an Indian faction.

6-Chatii, or another German tribe, to offset the Sweboz and the Eastern Europe Domination.

7-Scythian Neapolis/Crimean Scythians/(Bosporans?).
Would be interesting to see a Balkan Hellenised Steppe faction, no?

8-Emerging Faction Yuezhi
Kicked arse when they came onto the scene. As another poster said, the equivalent of leaving Mongols out of M:TW

9-Another Gallic/Celtic/Barbarian Faction:
Preferably in Eastern Europe, to remove Eleutheroi. Didn't the Makedonians get completely pwned by a Barbarian Invasion slightly before the game started?

10-Either a Celtiberian Faction (Arevaci), a British Faction (Eainn) or the other Numidian tribe, Massyli or Massaesyli. Imagine three-way wars over North-West Africa.
Just to "Mix it up"