Even if some place have a great climate to live in other factors will nullify it from becoming the most populous urban center even in future.Great urban center flourish and will flourish at the cross roads among easy water borne transportation hub,center of trade and commerce,large population nearby,easy availability of food,water and other necessities.You can built large urban center in middle of desert by using modern technology,but there is a limit,water constrain will hamper growth after a certain period,not to mention the prohibitive cost of all basic necessity as most of the things will have to import from a long distance.This is one example.
Bangalore may have good climate to live in but I think Mumbai will always be most popular among the Indian to live in due to so many other factors,Bangalore can not suppress Mumbai in either economy,size or in importance, comparative cost benefit analysis will not allow it against Mumbai.Easy water borne transportation is a great factor to influence the development of cities,even now and future.99 percent global trade happen with water transportation and cost increases with each kilometer distance from the coast or river port.It is no coincidence that most of the large urban center happen to be in such places.Dhaka is the most optimum place in this regards.It is the center of most dense population in the world,easy access to sea by Ganga-Brahmaputra river system, have great mighty rivers surrounding it,good source to have water for tens of millions of people as well as a acts a barrier to any land based invasion.Food, water,clothing,housing materials can be transported to it from a short distance and in scale that other place will find it hard to match in cost effective ways.Surrounding dense population will ensure it to be a center of trade and commerce resulting in big growth.It is also at the center of half the global population and sufficiently near to future largest economy in the world,namely China,India and South East Asia.So I see Dhaka is a great population and economic hub waiting to be happen.
Most optimum location are already mega urban areas.I think,other than Dhaka other optimum places are Shanghai,Guangzhou-Shenzhen-Hong Kong agglomeration,Tokyo,Mumbai,Cairo,Istanbul,Lagos,London,Buenos Aires etc.