If HK can be portrayed as the model of what PRC does to dominate, suppress, and assimilate lesser economic powers, and its occupation of Paracels and Spratlys as an overture to securing absolute control over all economic resources in the South China Sea, the neighboring nations will likely line up behind the US to discourage a hot military war, and then do everything they can to close ranks diplomatically and economically to keep PRC from taking pieces of their pie.
The mass-internment of Uighurs is also likely to spur the Muslim populations of Indonesia and Malaysia to wrongfoot China diplomatically and raise international support for sanctions.
China's main crime is carrying a really big stick, and speaking loudly instead of softly. If a country uses its strength too much, then it starts creating problems that only greater shows of force can fix. All that work on soft power in South America and Africa could go straight down the drain.
Imagine the United States' response to a covert campaign by Russia to arm protesting secessionists in Manhattan.
It's called a proxy war. Literally every other regional power is salivating over the idea of a massive thorn in China's side that a) gets them slapped with first world sanctions and b) gives them less free time to bully everyone else in the region. You're kidding yourself if you think all their intelligence agencies aren't coming up with shovel ready plans to get the the protestors the things they need if they decide to become freedom fighters.