It sounds like they don’t want to focus on one conflict in the next DLC. They mentioned an Empire that grew slowly, which implies that you will play the rise of Rome over a longer time period.
If they start after the death of Alexander then Pyrrhus would be a good start into Roman campaign that is also a good connection to the Alexander campaign. The main focus will probably be the Punic wars for sure. The Alexander campaign also started with the wars of Phillip against the Scythians and Greeks before going over to Alexanders conquest of Asia.
My guess is that they will go from Pyrrhus until right before Caesar. Though maybe you get more scenarios as the enemies of Rome compared to only 2 scenarios where you don’t play the Macedonians in the Alexander campaign. Hannibal is just to cool to not give him multiple missions.
The developers of Chronicles don’t want to use AoE2 civs. They have only used a hand full of AoE2 units so far. The Bengalis would have been the perfect civ for representing the Indians with their ancient Chariot UU.
Also the AoE2 Romans are a 400 AD civ not a 300 BC one. They are very bad at representing early Rome.
Sparta and Athens are pretty different in many ways and also you play both of them for long stretches of the campaign.
Also both of them have been used to represent a lot of other civs like Ionians, Thebens and all kinds or mercenaries and pirates.
Rome was a very big, long lasting and influential empire. We are literally using Roman letters right now, Roman calender, most countries have Roman law and many other things. But we only got 2 Roman campaigns since the release of Rise of Rome in 1999, and that’s only if we count the Byzantines. And that one Roman campaign is in Return of Rome so basically also AoE1.
China and Japan are in AoE1, AoE2 (4 different Chinese even), AoE3, AoE4 and AoM.
Persia is in AoE1, AoE2, AoM and now also Chronicles. Still missing in AoE3 which I’m personally pretty sad about (you can find many of my posts asking for Persians in AoE3DE).
Romans are in AoE1 and AoE2. If we count Byzantines they are also in AoE4.
Chronicles is based on the mod “Rome at War” so it was pretty obvious that they would eventually do Rome. Rome fans didn’t really have much Rome in AoE yet and Europe is generally very underrepresented in AoE1.
I’m pretty sure we will see a Parthian civ in Chronicles eventually if the keep making DLC. Rome at War had the Achaemenid (as Persians), Seleucids and the Parthians btw.