As for Tokyo, Osaka and basically any Japanese airfield with a paved runway, you might want to take a look at the Japanese Airports series done by Overland and Simmer's Sky. Might not be up to par with the latest creations by FSdt, FT and the likes, but I still consider them pretty decent and far better than nothing. Even more so when you keep in mind how sparse the Far and Middle East are generally covered scenery-wise, compared to Europe and Northern America.
As far as the rest of the world (Minus most of the north/western hemisphere) is concerned, it's all about having access to decent source material, ie hi-res aerial imagery to work into ground/object textures, detail shots/3D plans of the various structures and buildings around the place, people knowing the ins and outs of the airport in question so they can aid in creating accurate animations/AFCADs and beta-test the whole thing afterwards, etc. You will need people with unrestricted access to the air-side of the airport, otherwise it can get really tough nailing those little details that make or break it in today's top-class sceneries. Add to this more or less restrictive rules regarding the use of cameras in public for most of that countries and you're in for a very hard time sourcing decent source material for let's say, an chinese airport. Finally, it's an economic question - enthusiasm and a handful of mails saying 'thanks for the decent scenery' won't feed any payware developer. They have expenses that they want/need to see repaid - be it the money they've spent on getting allowance to use that aerial image in their scenery or all the time they've spent at their PCs creating seasonal textures from that aerial or getting the 3d model of that really creatively and complex designed terminal building done with minimal polygon count/frame rate hit. And of course, you would want to get yourself something nice from the money you've earned with that scenery. And seriously, how many people are going to pay for a Beijing scenery?
As much as I'd love to see the premier chinese airfields covered in FSdt quality, I don't see it happen anytime soon. Which is a shame really as flying in chinese airspace alone is quite thrilling and unique, let alone flying in and out of busy airports like Beijing.
