Making changes of this scale takes time, and it takes a unified will to make change. The hardest thing in the world is to say "25 years from now, if we do all these things, this will be greatly improved." It is made hard because people cannot easily see slow change, and they often are unwilling to wait so long for change. Making the change instant is very expensive and also hard to pull off.
Imagine some group that could decide to take about 15,000 hectare of land and decide to build a city[1], from the ground up, with current building standards and codes. They would have to start with a way to power the city. So building infrastructure to bring fuel to power plants and assuming a modern city of 2 million souls, call it 1.5GW of reliable power (so closer to 2GW of capacity so that plants can be off line for maintenance and you still have power). You'll also need to develop a water source, and water treatment facility. You can go the Israeli route and desalinate water for this city (constrains locations) or pump it to it (adds to the power budget). At this point it would be easiest to add a subway system (you can do it by digging trenches and then covering them up, easier than boring tunnels under existing buildings) which means you also have to have some of the basics of what your city is going to look like laid out, residential areas, industrial areas, high tech areas etc. Since you have the benefit of looking at problems in other cities, you focus on making travel within the city as "car free" as possible so that individuals can either walk or take transit. You maximize people space. Now you build an airport, something which can handle both cargo and passenger traffic at the same time. To start bringing in people and materials while the rail system and a connection to the highway system is built.
Anyway, you can follow this along and realize you'll probably need a couple of trillion dollars worth of GDP to go from bare ground to "modern" city, and it will still take years. There are examples you can look at in China of cities built from the ground up. There are probably things you can learn from that. Someone more logistically astute than I am could come up with a "molting" approach where you first cover the area with tents, then as you build things you remove the previous layer and replace it with a more improved layer. You might be able to go through several re-development cycles to get to the final product.
Or you can try to take an existing place and go over it from the ground up and make it into something awesome. That latter path takes a lot longer, decades.
[1] That is a bit more land than is available in San Francisco