Oh, well since we are on the topic of Hellenistic armies... here's my suggestion:

I strongly recommend the introduction a melee worthy light infantry unit for all factions that depend on the phalanx. Ever since Alexander's time, the need for light infantry to complement the phalanx has been well known.

As yet, the Seleucids are the only ones with a competent non-phalanx melee unit. I think the Macedonians should be allowed to train Thracian light infantrymen (not armed with falxes and with clothes!). For the Greeks I'm not too sure what to add. I mean, they were pretty die hard phalanx people and did not have a tradition for sword-armed infantry.