Gallic Chariots: I think they were added shortly after the Britons were cut. I added the current Woad Warriors and the Chariots to retain what was unique about their unit line-up.
As Hippias says the Gauls are known to have used chariots in the battle of Telamon (Etruria, 225 BC). That's a stronger historical source than we have for many of the units in the game.
Chariots would have been used by the wealthiest Gallic warriors, so they would have had the best armour available. Making them javelin chariots is about as realistic as we can get within the constraints of the game engine.
They could probably do with a name change though - as they certainly weren't "heavy" in the sense that the eastern/greek scythed chariots were.
Carthage rebels: High on my list of things to add are some new civil war scripts. I think there is a lot of potential for an interesting civil war with the Carthaginian faction, so if the new scripts work out the Carthaginian rebels will stay.
Generic AOR units: Some of these units are available over very wide areas (Barbarian Infantry are available over something like 20% of the map) so there is no way to avoid using generic names. We could of course break them up into more unit types with more specific names - but there are many other proposed changes that strike me as more urgent.
Epirus: As I have said before, I have reservations about adding Epirus, but it is the most popular request.