The Arverni god-king would make the writeups quite interesting.

Personally, I think that Carthage is a big no-no, because fighting the Ptolemaics over African dominance would be a major pain in the rear side, and Braden has just done a Carthaginian PBM not so long ago.

A minor faction would be more interesting, such as Pontos and eventually evolving into a threat to the rest of the world like Mithridates' Pontos was to the Romans.