Arcology

In one of the versions of Sim City, your city got to the point where it could build arcologies: super-buildings that were a self contained environment.

And now, this:

Sky City will boast a hospital, a school, 17 helipads, and enough apartments to house 30,000.

Above the world in 90 days: China building world’s tallest skyscraper — 220 storeys — in just three months

Just think about living there - the social aspects aside, I can't believe they can run water for that many households. Can you imagine taking a shower on one of the top floors? I know we need more urban density, but I don't think this will work. In 30 years it will be a slum, just like many of the huge housing projects in Britain, and for the same reason. The Brits committed what one writer called the "arithmetic heresy:" the idea that if 8 families in a block of flats could live together in good community, then 800 could do the same in a skyscraper. The Chinese perhaps have stronger cultural and social norms; but 30,000 people is a town, not a neighborhood. The building will need its own mayor and police force.

On the other hand they won't need a gym. Just going for a walk up and down the stairs will keep everybody fit for a marathon.