China is needed to properly represent the interconnected Eurasia that existed in the Middle Ages- the trade-networks and cultural influence was great. However, the Devs would need to consider two things: being able to make it run much, much faster, and being able to make it feel connected to the rest of the map.
Have all Eurasia and northern Africa, and the game will be complete- each constituent part cannot be properly modelled without all the other constituent parts of a system. Indeed, because of this, East Africa would be nice too, but that's less important.