some suggestions for newe factions:

*Western Germanic Faction e.g. Chatti or Cherusci to prevent a Italia/ Graeco/ Gallo-Germanic Empire
*Eastern Germanic Faction e.g. Bastarnae (suggested before) or maybe Neuriji to challenge/ force the Sauromatae to expand (in most games they remain dormant; like my latest Makedon campaign it's already 180BCE and Sauromatae only captured 1 city and lost another to Pahlavi)
*Illyria (for about the same reason as the Western Germanic Faction)
*Numidia/ Berber Tribes, Maybe an expansion of Africa, Carthage had some colonies along Africa's west coast founded by Hanno
*Illyria (as suggested earlier)
*Rival faction to challenge the Casse in Britian
*Aksum/ D'mt/ some Ethiopian faction
*Another Steppe faction such as Massagetae or Dahae
*Nabataeans to challenege Seleucid expansion into Arabia
*Galatians to bring more conflict into Anatolia and possibly waging war with Pontos or Seleucia
*Bosporan Kingdom to challenge Sauromatae and Hayasdan
*Maurya, Pandya and Yuezhi (If there the map expands east)

I think Gaul is already crowded enough with 2 factions, Syracuse would also not be a good idea because it would get destroyed very early (according to Cybvep)
Greece is already crowded enough and to make a new faction there (e.g. Aetolian/ Aechean League) would cause lots of trouble


p.s. why does Koinon Hellenon represent the Chremonidean league (according to EB's website)? the Chremonidean war did not start until 268/269 BCE