May I interrupt you with some wild guesses?

Hopefully:
- one of the various celtiberian tribes already mentioned
- a second arabian faction
- Kimbri
- an ethiopian faction (as far as my knowledge goes there where quite a few links to certain culture groups that are already in the mod ... )

Probably:
- Belgae
- Arevaci
- Helvetii, Rhaetii or something similar
- Atropatene