China hasn't become a Western capitalist democracy, but it has changed enormously for the better from the genocidal tyranny of the Mao era, and my guess is that it will keep changing.

One "first principles" way to think about it is that money is power, and as the Chinese middle class grows bigger and richer, it will have more and more of the power. I expect it will want similar things as the middle class in other countries.

This may take any number of decades, which unfortunately makes this a hard theory to falsify.