I used to propose a Sogdian civ in my concepts, while at the time there was not many people interested in the Sogdians in the forum.
I’d be happy if you are interested in this.
There, my suggestion to the campaign of the Sogdians was based on their city-states’ resistance to the Muslim invasion, and my suggestion to the campaign of the Chinese was based on the story of Yue Fei. I tried to present the tragic feeling of the Sogdians and Yue Fei in their battles against the invaders through the campaigns.
As for the An Lushan Rebellion, I had also proposed it in this another topic of mine. But, it is a historical scenario named to “Chang’an” rather than a full campaign, and the player is going to act Li Heng, prince of Tang, who gonna suppress the Rebellion instead.
If An Lushan become the campaign, I agree it could also be fun.