176 km. Why don't they make a 1 kilometer proof of concept then plan the other 175 once they've ironed out the kinks?
The purpose of this thing is not economical, or political, or social - the purpose is to satisfy the ego of an autocrat, and as long as that ego is getting stroked, the money will continue to flow.
They have many already, all of them unfinished and unpractical. And then the money moves on the a new city of the future.
I think is basically just a status competition 'my city is gone be a revolutionary design'.
The guy after MBS will likely try a city in a spiral or something.