If cities improved productivity by bringing more people in contact with each other, imagine everyone able to connect from anywhere. And without leaving their local communities, so there's no brain drain and less social atomization.
Unfortunately, none of our cities seem to be able to be able to grow without housing getting more expansive and traffic getting terrible.
Perhaps once we get really good at asynchronous work, the opportunity will be on the table for one city to try to import substantial numbers of people from all across the world.
Singapore is probably about as good an example as any (at least outside of China) of centralized urban planning (and they even have an interesting gallery on it https://www.ura.gov.sg/corporate). But, while getting around Singapore works pretty well, it's certainly not a city you would call especially affordable in general.