DH is Darkest Hour. But I have a better idea. Write them up in event form and I'll package it with my Cold War Tech Tree. MIB seems inactive these days. In my own mod I've incorporated many CCIP ideas though I've added my own wrinkles.
2) Interesting, will have to study further. It can be argued either way.
3) Actually Sheng Shicai was very mercurial and just wanted to be on the side that could give him power. He actually deserted the Soviets when the war with Germany initially went bad. I have no problem with him choosing to collaborate with Japan if the ai chooses this. In my own modding I have East Turkestan as the state to be released if there's nothing in the area. Mohammed Ali Bughra would be a very credible Japanese collaborator. He was leader of the First East Turkestan Republic. Japan was known to cooperate with non-Chinese ethnic groups in China.
4) Maybe that should be up to individuals to create their own events
5) One of my interests is the 1932-36 series of mini-wars between China and Japan, most of which ended with China signing a humiliating peace treaty with the Japanese. If you're aware of that history it's impossible to believe anybody but known collaborators (most of whom collaborated with Japan because of grudges against Chiang or because they lost out in the warlord wars) would cooperate with Japan, or that Japan would trust them. So while in my own modding Japan can still release these warlord states, they will be faceless and missing a few leaders. And of all the warlords, the Ma warlords were the ones that hated Japan the most and also the ones Japan feared most, because they actually butchered some of the Japanese soldiers they captured, and Japan didn't want to fight them after that. Yes I'm sure Japan would find people to work for them, but most likely most of them would be people we've never heard of.