Tokyo, Japan, with a current urban area (as opposed to "city proper") of 39.6 million people, is currently the largest city in the world.
Is it likely that there ever be a city on Earth that has at least 100 million people in its urbanized area?
If so, approximately when would the first city on Earth to have more than 100 million people in its urbanized area be likely to cross that threshold?
And, which cities in the world are the most likely candidates to cross the 100 million threshold?
BONUS QUESTIONS: What would be the answer to the questions above be if they were applied to the United States of America, rather than to the entire planet?
What is the largest city that could be sustained on Earth assuming no profound breakthroughs in technology from that present today or just around the corner in developmental stages today?
This question assumes nothing counterfactual. It is about the real world Earth and the real world United States, in the foreseeable, predictable future.
Feel free to consider the possibility that a large city arises because cities that currently have separated urbanized areas that are separated by non-urbanized areas grow together to form a single urbanized area.