Forget Taiwan, its Japan that China would love to settle scores with. I wonder how SK would feel given their own experiences with a militarized Japan. That’s probably one of the few things other East Asian states agree with China on.
Not to say they’d do that again today, but then again no one thought they’d do what they did when they first became a military power in the early 20th century. Still, it’s possible things ramp up for Japan given they’d also be a deterrent to Russia.
Of course, China is still pissed about Japan, and we all know Japan was on another level, but Tawain is the first choice due to the location and it being former people of China who broke off from the Communist regime. Let's not even discuss the financial implications of a China ruled Tawain.
North Korea is a pawn in the America backed South Korea influence. This is why North Korea is allowed next to China with Nukes.