It would be really neat to see one of these mega city designs built in my lifetime.
Even in land-scarce Japan, if they wanted to start a city from scratch it would be easier by orders of magnitude to just clear-cut a forest somewhere first.
This thing is cool, but there's just no reason why it has to exist. There's plenty of land left on Earth to use first.
But in that scenario I doubt we would be able to pull off such project.
Seems like good sci-fi material though.
Imagine all the logistics to send food around. The cabin fever from living on floor 500 and basically never touching the ground.
It would be better just to build smaller buildings.
Your comment reminds me of a fascinating book I have, Cities Without Ground: A Hong Kong Guidebook. It is full of cutaway diagrams of different areas of Hong Kong showing how you can get around from one place to another without ever touching the ground.
Like Sai Kung: "...Even at the water's edge, ground is elusive..."
We may not be able to simply build anywhere we wish on a given planet, and the horizontal sprawl of "traditional" cities in unexplored and potentially hostile environments would be risky.
Having a single place for spaceships/landers to dock at/orbit over, right next to the facilities for refueling, cargo transfer, storage, processing, distribution etc. would be desirable, so more-or-less vertical megastructures may be more practical there.
Perhaps a city in international waters could be built without anyone's permission, and outside any nation's jurisdiction.
Does anyone with expertise know if this is true or not?
That's the goal of the Seasteading institute.
Because major cities are located near natural supplies of fresh water, navigable waterways, etc., for a reason. The good places for cities tend to have cities in them.
The places that don't have major cities have good geographic reasons for not having major cities. Pouring money into building a major city in the middle of Nebraska,or a similar location, would be silly.