As @NaiveCarto said we add China region to IU and use system of HRE to show China's political and diplomatic situation in that era.I just wanted to tell you we have read the thread and will keep reading the comments.
While personally I like the idea of an china expansion, I can say we have no expansions planned at the moment, and we are working hard toward an release and after that we will look for expansion ideas. I will NOT (and can not) promise anything, but I can thank you for providing an interesting read about chinese history, which I didnt have much knowledge about.
Many players think that China is a difficult area to produce because, first, China has too large a provinces, so that in EU4 there are many ways to limit the expansion of the already unified regime in China.
This is actually a better solution in the historical context of IR or IU. At this time, China is in a state of long-term political separation, just as in the early modern Europe and Japan in the Shogun era, although these countries in China There are cultures and religions that are shared, but political entities are independent of each other, so provinces is not a big problem.
The second is the ambiguity of Chinese historical data. Compared with European producers, it is more difficult to obtain second-hand information about China than to read Chinese materials directly. This is like the Chinese MOD production team wants to make a European linguistic materials for Chinese translation are largely required for European MODs.
If this is needed by the IR/IU production team, you can contact us and the enthusiasts who are active in the forum to provide research by relevant sinologists.