I really hate to say it, because I actually really like the idea of a game encompassing all of East Asia, but you have a good point there. I was actually thinking that part of the problem with an East Asian game is what time period to set it in. Granted, outside of China and Japan I'm not terribly familiar with East Asian history, but at least with those two, the most interesting parts of their history tend to be about internal issues. Barring a few obvious exceptions, international events usually aren't taking center stage. Mostly, I think, because of China. When you have such a big, culturally dominant power around for at least a couple thousand years, they tend to pretty well occupy everyone else's attention, and the times when that breaks down are generally because of internal events or trends in China. So most of the time periods we choose are naturally based on what's going on in China. But just because the Three Kingdoms period is fascinating and deserves a game in it's own right, doesn't necessarily make it interesting to play anywhere else. I couldn't really speak for Korea or any of the other Southeast countries during the time period, but at least anyone who wanted to play in Japan would be frustrated, mostly because it was still in the process of becoming a thing, and the oldest Japanese sources for the time were basically just making shit up.
I think, weirdly, Western GSGs kind of have an advantage in this regard. If an amateur interest in history has taught me anything it's that Europeans up until just recently spent most of their time thinking about how best to kill the other Europeans, and they spent so much time beating each other up that international strategy just plain becomes more exciting than "Do whatever I can to not piss off China while doing my thing, unless they're weak and/or I'm Genghis Khan".
