China

[True Federalist (진정한 연방 주의자)]

It is likely to seek to follow the Singapore model, but I doubt it can.

China is simply too large.

A federal capitalist oligarchy in the mode of Mexico under the PRI, circa 1950, is one likely possibility.

[True Federalist (진정한 연방 주의자)]

If any breakdown were to occur, I would suspect Tibet and the Western Muslim fringes of the country would but the Chinese government is clever to encourage Han settlement in places like Xinjiang and Tibet.

You mean like how the Soviet government was clever to encourage Russian settlement in the other republics of the USSR?  Thanks to the one child policy, I suspect that there will be significant re-migration of the Han back to the traditional Han territory once their demographic bubble busts and the flow of rural migrants to the cities slows because they've run out of people to go.  Won't happen for several decades at least, but it is likely to happen.