There are over a million legal immigrants in China, plus an unknown but sizable number of illegal immigrants, mostly from Vietnam and Myanmar. Of course this is not a huge number compared to the overall population, but it's still a sizable number of people.

The villagers are treated as immigrants with preferential treatment for city-born folks.

They indeed will be in about 20 years when the impending population collapse hits

Not really. China is essentially a microcosm of capitalism playing out entirely internally.

E.g. to move to the capital permanently from outside you're basically under the same scrutiny as an immigrant on a greencard.