An Alexander era game would be awesome, if they redesign the Rome concept from the ground up.
Separate "court characters" from "all other characters in this kingdom". Make kingdoms and other polities more "ad-hoc" creations, rather than the fundamental entities that the game revolves around. Make battles matter more! Allow events to be triggered when you are losing a battle, or are winning, or upon losing it.
Find a way to interact with "barbarian lands", that does NOT rely on them being "polities"!!!! Stop treating barbarian lands as empty provinces with the occasional army spawn.
Allow on-the-fly creation of "alliances of convenience" - as in, let the player contact an AI nation and ask whether they want to be part of an attack on a neighbour, within the next 6 months. Stop treating all alliances as for-life-compacts.
Let the player have some sort of influence on training and organization of the armies that are levied from the provinces. Let there be a difference between calling just the nobles and their retainers, and calling the peasant / city levies.
And: Let there be fun with "roving characters", i.e. guys who travel across the map, going from one court to another. Like, mercenary captains, prophets, exiled leaders.