They might add in a new government type for China, but it honestly seems like a lot of work when they're only adding in one, typically minor, physical realm to the game. Especially when this"Western Protectorate" (or whatever it's called) isn't the actually run by the Emperor, just one of his agents.
So, they could probably say that the Protectorate's relationship with the Emperor isn't really feudal, but the Protectorate itself functions basically like a feudal realm-- in the event that they didn't want to go through the trouble of coming up with a whole new government type. My money is on them not taking the trouble.
There are various ways how the Western Protectorate can be handled.
After all, apart from the possible interactions and the new governments, this is the biggest and most interesting question about the upcomming DLC for me.
As suggested somewhere else, the bureaucratic system could function numerous ways without having to be so performance heavy. I really don't know the chinese system, but there is plenty of inspiration in the Byzantine or islamic world, which had bureaucratic systems too, with prominent families taking offices, powerfull slaves or eunuchs, standing or slave armies often more faithfull to their general than their ruler.
All you need to do is to give those characters a platform on which they could function. In islamic world it might be
tribalism, in Byzantine world dynastic palaces, slaves could work around
slave market and mercenary/standing army companies, etc.
Not sure how you'd strike back in a meaningful way if the provinces for the main Empire aren't on the map. Nowhere to march any armies.
Sure, you can take back the provinces that China invades, but that sounds pretty darn unsatisfying.
How else do you figure you could strike the main Empire? Maybe they'll throw in a few events. Even if they have you a real big one like assassinating the Emperor, you won't really get to see the fallout. The best I can see happening is an event that says "Oh boy, you got them good... You should see it. Chaos. Pain. They're real sorry they messed with you. Honest."
There are many possibilities. Some kind of simulated war window, a separate schematic minimap, where one would be able to take some land? Or it could be war-tied decisions where you can pick for instance - go and take their land which means entering a battle on their (abstract) territory and taking their capital with high attrition costs and risk of total anihilation unless you send a doomstack?
Who knows, we know so very little..
