I have played Age of Empires IV for more than 600 hours and purchased almost all of its DLCs.
The civilizations I’ve played the longest in the game are China and its variant civilizations. Every season I use them to reach at least Platinum rank. I think the three China-related civilizations are all very well designed, and they integrate the characteristics of real Chinese civilization very well, such as the Imperial Official and the dynasty system, which make the game highly immersive. The two DLCs that include Chinese variant civilizations — “The Sultans Ascend” and “Yue Fei’s legacy” — are also my favorite DLCs. So I hope the team can release more China-related variant civilizations.
I would like to put forward an idea of mine here: to release two civilizations — a new civilization, Korea, and a Chinese variant civilization, “The Legend of Qi Jiguang.” The background would be the war on the Korean Peninsula from 1592 to 1598 involving China, Korea, and Japan. Many heroic figures emerged during this war, such as Yi Sun-sin, Chen Zilong, Li Rusong, and Shen Weijing (who entered the Japanese military camp alone and delayed the Japanese attack). The latter, Qi Jiguang, is a legendary figure in China, and his army was known as the Qi Family Army, which is very well known in East Asia. These would be very friendly to the East Asian market.
Speaking of unit design, Korea needs no further explanation — it could include a modified version of the Nest of Bees and the very famous Turtle Ship (both designs can fully reference precedents that already exist in the Age of Empires games). Also, Korean archers were extremely powerful, so a unique archer unit with special technology could be designed. In addition, there were the righteous armies active on the Korean Peninsula at the time — peasant militias that spontaneously rose up to resist the invaders — which could be made into units produced through some kind of conscription mechanic. As for landmarks, there are Gyeongbokgung Palace, Byeongsan Seowon, and Sangdang Sanseong, among others.
As for Qi Jiguang, the first thing that comes to mind is the Qi Family Army named after him, which includes a unique spearman unit called the Wolf Brush (Lang Xian) — a rather exaggerated-looking weapon made from bamboo — which could be researched as a unique Barracks technology, with the effect of reducing enemies’ attack speed and movement speed. They could also form a unique formation with samurai and archers — the Mandarin Duck Formation — providing a defensive bonus. There is also the special gunpowder unit, the Hu Dun Pao (Crouching Tiger Cannon), a unique Chinese unit similar to a small mortar, which could be designed similarly to the Japanese Ozutsu unit, with bonus damage against buildings and siege engines and very convenient mobility. As for cavalry, there were the Liaodong Iron Cavalry active on the peninsula at the time, which could be made into a shock cavalry unit positioned similarly to the Byzantine Cataphract. As for landmarks, there are the Temple of Lord Guan, the Temple of Heaven, the Imperial Ancestral Temple, and so on. The Imperial Official system could be retained. The above designs are my suggestions, and I believe the development team will come up with even more polished and interesting designs! I am very much looking forward to it.