Originally Posted by
Magister Militum Flavius Aetius
The "Theme system" was actually just a method of recruitment that originated under Valentinian II in 386 and was re-implemented by Charlemagne and Nikephoros I. But yes, we have plans for other time periods eventually, including the 8th Century. Unfortunately Attila's map is not exactly conducive to an eastern-focused campaign, barring the Grand Campaign map. We may look to Rome 2 Total War for some campaigns as a result, such as a 3rd Century campaign.