3) A lot of background research would be needed - I think Paradox are capable of this, but maybe a regional developer (e.g., Taiwan/HK) might make a better job of it.
Some things on the Far East in EU4 might cast doubt on that
But hey, as has been pointed out, you could make a mod for CK2 aiming to model China. This would be no more labour-intensive than the GoT mod has been.
GoT was however modelled upon Western feudalism, which CK2 was developed for. I'm not saying it is harder to apply the game to China than it was to create Westeross, but many things are certainly considerably different.
For example:
Inheritance: Inheritance was Agnatic Primogenitre, but with the wife's sons taking precedence over concubines, with the possibility for rulers to bypass the rule.
Army: Spring and Autumn armies were limited to 3 armies for major powers, 2 for medium powers, and 1 for minor states, of 12,500 people each (at least nominally).
Army II: Spring and Autumn states operated citizen armies, in which conquered peoples and farmers were not eligible.
Army III: Warring States armies were mass peasant levies and could not be raised all the time unless the country was sufficiently stocked with supplies and food.
Warfare: Long term wars (~months) were impossible to finance and logistics were a massive limiting factor.
Warfare II: Spring and Autumn states were essentially city states vying for farmlands that should be won and lost at little cost (warscore).
Warfare III: Warring States states transitioned to building cities for more effective rule; control were based on whose armies were in the city.
Sieges I: Defenders often fortified large armies within major settlements, which were not easily taken.
Sieges II: Mountain passes were hugely effective chokepoints that could not be easily by passed by, well, walking through them.
Administrative I: The central government ruled the country directly with appointed officials, rather than feudalism.
Administrative II: Powerful nobles existed with hereditary estates and private armies, and tried to co-opt public lands into their private domains.
Administrative III: Population was important; losses on the battlefield was expensive to replace and directly harms productoin.
Politics: Tribal politics dominates the Spring and Autumn period especially smaller states, which constrains the ability of rulers to wage war etc.
Diplomatic: Spring and Autumn international affairs were dominated by the major states attempting to become hegemons, collecting nominally sovereign satellites.
Just some things off the top of my head. Some of these could be modelled, and others could be ignored. But, the inability to garrison a large citizen army of the nation at the capital, for example, means that small states could be ahistorically easily gobbled up - even if maintenance were raised to model the inability of states at the time to actually field armies for any length of time. That's not to say CK2 doesn't have a very good framework already. It definitely does. But there's limits on what you could do with modding, unfortunately.
