In the midst of a depression is not the ideal time to talk about housing developments, especially when the depression was caused by housing speculation. But here goes anyway ...
Detroit has seen numerous attempts to "revitalize" the city since people realized how much tax revenue disappeared after the white flight of the 1960s and 1970s. Many of these attempts have included proposals for mixed-income housing developments in or near downtown or the riverfront. For any of these revitalization efforts to have a chance of success, however, they cannot include mixed-income housing.
Rich people pay a lot more in taxes than poor people. If you want rich people to pay taxes in your city, you have to give them an environment where they do not have to work harder to stay rich just because of where they choose to live. If you tell them that they have to live with poor people in order to live in the shiny new downtown development in your city, they will not choose to live there. They have a fear, right or wrong, that the poor people next door will take their belongings if given a chance.
Affluent housing areas have a way of preserving and breeding other affluent housing areas nearby. Look at the West Village district. While it is not "rich", the preservation of wealth in the adjacent Indian Village neighborhood has stabilized West Village. But because it is not buffered from the poor areas of East Grand Boulevard stretching up to and past Mack, it has not prospered to the degree its excellent housing stock would predict.
The riverfront, the Cultural District, and Brush Park should be valuable and expensive areas to live in. Why have they not developed into a high-cost housing districts? My contention is that every time the powers-that-be in Detroit talk about revitalizing an area, they start talking about how it has to directly benefit all Detroiters (i.e., poor people, too). I'm sorry, but there are square miles upon square miles of available housing in Detroit. The shortage that affects them the most is employment, not housing. If you can successfully create a large high-rent district close to downtown that is buffered from concentrations of poor people, you will create jobs that will benefit all Detroiters.
The next time some community leader mentions "mixed-income" when talking about Detroit development, ask them why the upper-income segment they are targetting as customers would want to participate. And if they have an answer for that, ask them why the development should not cater completely to that upper-income segment in order to maximize the benefit for the backers of the project.