I voted "no" as I prefer settings on the rough and tumble borderlands, and I am not that much of a fan of the OTU anyway.
Can I ask why you picked these 4? They have among the weakest demographic outlooks globally, according to UN baseline projections. Russia's population is projected to fall by about 15% by 2100, China's by a third, and Japan's by nearly 50%. I can't find the number for (South) Korea immediately, but their fertility rate dropped below 1 last year (replacement is about 2.1). Except Russia, none of them attracts much immigration (although Japan is talking about allowing more, but even then only for relatively short-term work passes). Russia and China are still classed as emerging markets rather than developed (Korea is still in some EM financial market indices although that is mainly a legacy thing, they are developed in terms of incomes, although still poorer than Japan).
That said, there is a dramatically widening uncertainty band around the demographic projections the further out you go, and geopolitics can upend everything, e.g. Russia could get some of the USSR back! Or Korea could reunite.
Plus, rule of cool trumps all, if you want those 4 then why not go for it. A "sensible extrapolation" might be pretty bland. Whereas something like 2300AD's French-dominated setting is very cool because of its originality.
The RF has a long lead in space.
China and Japan are among the world's largest economies. Both have significant space programs.
And climate change may actually benefit Russia, overall. Russia is also showing some signs of a civilizational rebirth, at least in my view. China has leaders unafraid to think big and to spend a lot of resources--and lives--on major projects.
Low fertility and shrinking populations would definitely impact these nations' economies, as such factors will with Europe, but it seems plausible to me that robots and AI could increase productivity per worker enough to offset that decline.
And, yes, I assume Korean Reunification. Korea is the outlier in my lineup, I'd say.
I could see any or all of these countries declining in the not distant future, but I could also see them becoming/remaining (Russia and China) major powers. Russia is the most plausible case.
I grew up with some exposure to Russian, Korean, Japanese, and Chinese cultures and people in Portland OR, which might have been a factor in my choices for making Traveler stuff.
Please don't mistake me for any sort of expert. I once took a Russian language and culture class as a kid. Do I speak Russian today? Ha! No, not at all. My sister-in-law is from Hokkaido.
I once hung out with Chinese sailors my mom brought home. No, really. They were drinking beer in the Safeway parking lot and the security guard came out and started giving them a hard time (I'm not sure they understood the guy was not a real policeman). My mom pulled up and called for the sailors to jump in her car. Ten minutes later, these guys were in our living room hanging out with my parents, me, and my little brother. Language barrier? Yes. But we had a good time anyway. One of them swapped smokes with my dad.
Aramis speaks Russian, yeah?