On the topic of Manchuria and Korea
I've already said that both stay a part of Japan into the modern day and regional identities are maintained (and in the case of Manchuria), reinforced. But seeing as I haven't given the 'word of God' about insurgencies or anything of that like, I might as well do so now.
The time for answering these questions isn't in the 2000s (when Japan may very well be in a bit of a decline phase), but in the 1950s, when they are the ascendant power in the region. In 1949 the Chinese declared a third war against Japan in the hopes of reclaiming Manchuria (which at this point was still an 'independent' state, with the public allowed to vote on low-level district representatives although not yet the overall government). Japan comes to Manchukuo's defence and pushes the Chinese back, before developing a nuke in 1951 and threatening to bomb Nanking with it unless they agree to an immediate white peace, which they do (all per the final threadmark of the TL). Then sometime within the following decade, Manchukuo votes to be annexed by Japan once Puyi dies.
During this time, insurgencies in Korea and Manchuria are very much a possibility - if China and Japan are already in open war then there isn't really any reprisals possible beyond what is already ongoing. Japanese mistreatment of Koreans, particularly before 1940, is still fresh in a lot of peoples' minds, so uprisings would have some measure of popular support, and the IJA is already distracted fighting the Chinese army, so there's a much greater opportunity for disruption.
However Japan then wins the war, and any remaining rebel groups are going to be crushed by an angry IJA. Ordinary Koreans would come out of this alright (a big focus of the IJA after 1943 was disciplining rogue officers, and by 1951 I think it is fair to assume that problem has been adequately solved) - the Japanese government is trying to integrate them after all, but the majority of nationalist groups would have been disbanded and their leaders killed, which would weaken the movement for a good few years at least.
Contrast this with the 2000s. By this point, Manchurians and Koreans have been doing reasonably well for themselves under Japanese rule, and virtually everyone living there has never known any different (older Manchurians will remember Manchukuo, but that was still pretty much 'Japan' in a different coat of paint). They have the vote, and while Japanese have a plurality of the votes they do not have an absolute majority, so proposals that don't treat non-Japanese fairly aren't going to get passed. (The real 'victims' here are true minorities such as Pacific islanders, who don't fit neatly into the "three peoples" narrative that Japan likes to push).
The only power that really has anything to gain from a breakup of Greater Japan is the ROC, so it is pretty obvious that Japan's attention is going to be on them. The two are very much rivals and the land border they share is armed. The IJN is the second strongest navy in the world (after the USN) and controls the seas along China's coast (Vietnam, one of Japan's closest allies, hosts a Japanese naval base). Getting guns or money across that border is going to be difficult. Possible in the case of Manchuria (one can go through Russia), but extremely unlikely in the case of Korea, at least to any meaningful degree.
Because of Japanese efforts to support a "three equal peoples" narrative, Manchurians and Koreans can get most of what they want through the ballot box. The only issue that would not be ever passable would be outright independence (Japanese oppose it because maintaining the existing borders is seen as very important, Manchurians or Koreans would oppose the independence of the other because it hands control of the government entirely to the Japanese, who outnumber each group individually). So if they're going to rise up in insurgency-level numbers it would be if they want independence.
If Manchuria was to gain independence after an uprising, the remainder of Japan isn't going to be too happy with them about it. The sort of defence against China that occurred in 1949 won't be extended to a new Manchurian state which would be seen as traitors to Japan. The ROC would definitely invade as soon as they were ready - they were just as fanatical about "one China" as the modern PRC is, and while their army is about on par with the combined forces of Greater Japan, it is much larger than that of Manchuria alone. So Manchuria would very quickly be annexed by Nanking, whose first priority will be destroying this new Manchurian culture and making everyone Han - a fate most Manchurians would be quite fearful of. They also go from having 30% control of government to perhaps 5 or 10% with a much more united opposition. 30% can't be easily ignored, 5% certainly can. There's nothing really to be gained by rebellion.
If Korea was to rebel instead, they probably don't have to fear the Chinese as much (no land border, and not seen as "Chinese" by those in Nanking). However, a Korea that has made an enemy of Japan is also going to be in a lot of trouble - they're surrounded on all sides but one by Japan, and that last side is the East China Sea, which the IJN dominates. If Japan doesn't outright re-invade Korea (depending on the government in charge at the time, it very well might), they could easily cripple the state's economy with an embargo. Korea has also gone from the third most important player in a very strong state to the sole player in a relatively weak state, which is hardly an improvement.
People only tend to rebel when times are bad, and Manchurians and Koreans think that times under Japanese rule are reasonably good.
Then the Mig/Horten 229 seeing ACTUAL mass use and not being a nazi fantasy Wunderwaffe, is going to change factors a bit post war.
The Ho 229 'Flying Wing' isn't used ITTL. MiG uses a copy of the Me 262, and then a slightly smaller analogue of the MiG-15.
I never really said much about small arms but definitely agree that something like the MG42 would find its way into Soviet (and then Russian) arsenals.
- BNC