This is all my opinion, by no means this is a fact *Although i wish it was. I have been lucky guessing Pontus and the Greek City States as pre-order and day 1 dlc, so i wanna test my guessing abilities *

I think the next DLC will cover the following factions:

The Barbarians Faction Pack

Lusitani
Dacia
Sarmatians

it is probably going to be released around the Thanksgiving-Black Friday-Xmas-New Year days.

The next DLC after that one will probably be...

Eastern Factions Pack

Seleucid Empire
Armenia
Bactria

This might be the first DLC of 2014....
The east is empty, at least playable wise, so i am sure they will fill it up. Either this or the barbarian pack will be released first, will depend on fan demand mostly.

Around Spring/Summer 2014
Greek States Faction Pack #2

Syracuse
Pergamom
Rhodes

On the 1st year anniversary of Rome II or around Rome I 10th Anniversary we will probably get the first expansion pack.

The Punic Wars DLC

1. New Campaign
2. New Historical Battles
3. New units for Rome and Carthage.
4. Numidia as a playable faction in both the Punic Wars and the Grand Campaign.

After this, is really hard to tell what CA might be planning...