I could half replaced Detroit with (parts of) say Chicago or LA. Detroit is just more dramatic since the dysfunction took over the whole city.
In general, cities like Chicago and LA have lower crime then they have in decades, have higher property values then they have in decades, and are contributing a great deal to the economy on a per capita basis. Cities in the US in general are doing quite well right now.
In the 1980's, people often argued that cities were "decaying" and all that; the opposite is true now, young people are moving back to cities in large numbers, probably because the high crime rate that drove people out of cities 30 years ago is now way down.
Speculation is important for forecasting; it's also fun. Speculation is usually conveyed in two forms: in the form of an argument, or encapsulated in fiction; each has their advantages, but both tend to be time-consuming. Presenting speculation in the form of an argument involves researching relevant background and formulating logical arguments. Presenting speculation in the form of fiction requires world-building and storytelling skills, but it can quickly give the reader an impression of the "big picture" implications of the speculation; this can be more effective at establishing the "emotional plausibility" of the speculation.
I suggest a storytelling medium which can combine attributes of both arguments and fiction, but requires less work than either. That is the "wikipedia article from the future." Fiction written by inexperienced sci-fi writers tends to generate into a speculative encyclopedia anyways--why not just admit that you want to write an encyclopedia in the first place? Post your "Wikipedia articles from the future" below.