I was thinkin: will be amazing a satrapal revolt submod, in the revolt against artaxerxes, few decades before fall of empire.
with characters like mausolus of caria, artabazus etc etc for the satraps, and their allies, the greek mercenaries "warlords" like, memnon of rhodes, and mentor etc etc
Even with some script, for the cities that still loyal to king, and artaxerxes invading army.
It's been an interesting period for play. much.most of the same satraps, and their commanders, later have fight against alexander.
There also some unit to insert: in that period, greek mercenaries was much needed by satraps, and they pay very much for they, because they train the persian to fight like hoplite (kardaka), also if persian don't want adopt complete panoply. (greek mercenaries complain this sometime).