Ideally East Asia should receive two DLC-s with 3 civs each.
The first one should be Tibetans, Nanzhao and Gokturks centered around the Tang Dynasty. A Chinese campaign would fit here the best, perhaps a Korean too.
The second one should be Jurchens, Khitans and Tanguts centered around the Song Dynasty and the rise of the Mongols. A Japanese campaign should be added here.
Southeast Asian DLC could feature Siamese, Javanese-Malay split and Chams. Perhaps Visayans and Moluccans.
Finally, a Dravidian civ split should happen to Tamils (current Dravidians) and Kannadigas since both were very relevant and had multiple big empires. Oriyas would be another major Indian civilization covering the Gajapati Empire and the Eastern Ganga Empire. Perhaps a third civ, like the Sinhalese could appear, or the Deccanis.
Oriyas perhaps have the best campaign potential in all of India: Kapilendra Deva - Wikipedia