There is no detailed information about the civilization yet, but as noted by the moderators of the forum where the announcement with a screenshot appeared, several conclusions and assumptions can be drawn from the image.
For example, one can get an idea of the Byzantine army’s composition. Crossbowmen, spearmen, and knights are visible in the screenshot. Heavily armored cavalry can also be spotted. These are precisely the troops the Byzantines had in Age of Empires II—cataphracts.
There are several unique buildings. Four water reservoirs particularly stand out, seemingly connected by an extensive network of aqueducts. None of the existing civilizations in the game have such a water supply system.
The release date for Rise of the Sultans is currently unknown. It is likely a paid expansion, as it has a Steam store page.