I frankly just don't understand why someone would want China added to the game at this late stage. All it will be is a massive disappointment, and just be a reskin of feudal Europe. And for anyone saying "Oh, they'll just add new mechanics!", well, you can just look at the Muslims to know how that goes. They're essentially just Europeans with the addition of minor changes. Every nation in the game, regardless of where they are, still plays like a feudal European lord. The Muslims have been playable for 2 years now, and the decadence mechanic has still been broken for most of this time, only really getting a facelift in ROI. A dramatically new form of government for an entire map section is just not going to happen with the limited crew that is essentially watching over the game. And why bother with ~1 year of development, when they could be putting it towards something like CK3.
But I suppose the main issue is, what would even be fun about China, that isn't in the game already? The Song Dynasty had possible 100,000,000 people in 1066, which could easily annihilate any faction in the game. They could easily conquer the Liao at the gamestart, and could just steamroll the entire map. Also, they'd have gunpowder weapons far before the end of the game, which would be even more difficult to deal with. And this would be added to the difficulty of simulating the money gained from a city of 1 million people, which would mean any player would never have to worry about spending during the game. So let's say they do get nerfed, and can't really declare war on anyone. Then it'd just be a huge Holy Roman Empire, with maybe a few flavor events/decisions, like ROI.
China may have a large influence on the game map, but frankly, this just doesn't matter. Crusader Kings 2 doesn't simulate influence or trade. It simulates war and marriage. And frankly, the Devs removing provinces from the Abbasids in Charlemagne should tell you everything you need to know about Crusader King and Empires. It just simply can't handle states that go past the Kingdom level.