The internet may be the least they worry about. Xinjiang is big hot dense mess since a few years ago, terrorists and extremists are not rare in Xinjiang. The current state is more likely in a war against terrorism.
Their are a fair few cultural differences in China (even just within the "han race" let alone the other "races"[0].
But I often play the thought experiment in my head: How would the US govt react to the Latinos or the African Americans wishing to create a seperate state within the US?
I don't really see it playing out that differently to what China are doing.
Is this just a case of "China has a problem that we (the US) don't, and look at them struggle with it!" kind of thing?
The US period of herding minorities into sub-states called "reservations" ended a long time ago.