I fully annexed Yue in one war, and that made Changsheng my tributary. So two potential coalition members out.
Emperor Dai Viet was allied with Ayutthaya and I really didn't want to break our beautiful alliance that lasted the whole campaign, so I distracted Ayutthaya with some phony Malacca war and attacked Dai Viet for the mandate.
I dev pushed last Sichuanese province to 20dev, even though I somehow wasn't able to full core it. It doesn't really matter, as long as I get to accept any second Chinese culture.
Malacca got beaten and gave us some money with almost no effort on my side. War with Dai Viet was trivial as well - so now they can enjoy falling apart to mandate loss.
All potential coalition members (Ming, Shun, Korea, Wu, and barely Dai Viet) are annexable in one war and have no way to defend themselves, so that will be trivial.
The campaign is won.
And here's the culture mapmode after 120 years of simulation
All China turning into Jianghuai so fast is the thing I dislike about it
Elsewhere spread is reasonably paced
I'm disappointed by just how anemic colonization has been again
So some final conclusions. I'm a bit disappointed by Japanese mission tree. Like there's a mission to take or destroy empire of China - but it's gated behind one to conquer Manchuria - which requires control over every Manchu province directly or through non-tributary subjects. The whole point of China game is to have tributaries everywhere, so that won't work. There's another such in Kamchatka, even though that place is only good for tributaries. Overall, nothing special here.
I really liked playing as a custom nation. Coastal raiding is extremely powerful very early, but rapidly loses value with time, and it's tedious figuring out which provinces were or weren't raided.
I thought it would inflict significant damage on Ming, but it wasn't really enough. I also discovered that they patched the "blockade impact on siege" so it only affects coastal provinces now. That turns it from amazing into mediocre idea.
Once more, I'd play a lot better if I read nation specific missions and event before starting. As Vijayanagar campaign I could have dealt with Tamils before unpausing and have whole mission tree unlocked. As Japan, I could have dev pushed provinces which will get gold, as I was dev pushing for Renaissance and Printing Press anyway, and that would save me 4000 mana or so.
Not like I had mana issues - that 5/5/6 shoguness from event, who got the throne at age of 16, is still going strong at 64. Whole campaign and only 3 rulers, that's my RNG record. Beyond certain point I was also obscenely rich, so I could afford very high level advisors.
The mod to fix vassal missionaries just works.
Overall it was good fun.