I don't know if this question has been asked before.
It seems to me that the period of the Muslim conquests remained uncovered. This was one of the special periods of the "Dark ages".
Byzantine and Sasanian empires are gradually weakening. The dawn of a new empire at the same time. Formation of a new religion. These are interesting times.
I would like this to be a DLC to the Attila TW, because this game needs a new breath. That is how it was with Rome II TW thanks to Empire Divided and Rise of Republic.