Patman
Rodent of Unusual Size
The biggest problem in the long-term in the schools. You can get young professionals and artsy fartsies to live in downtown and midtown, but as soon as they get married and start thinking about kids, those people are going to bolt for the 'burbs unless they can fix the city school system.
The reason a lot of cities hang on is because they constantly replenish with college students in its urban core. Without the universities Boston would likely be similar to Detroit as has been witnessed by general state migration patterns. So with that core you have a constant pressure to maintain a quality level regardless of what kind of urban hell may exist. What separates boston from Philly is that a racial pandering taint never took root in Boston, save bussing.
As for Detroit... Young and urban is just a facet. It's more an indicator. Detroit cannot just jump to the end solution. Many things need to structurally change in the political culture and its unclear its gotten there yet.
I'm reminded of correlation causation. Just because QOL regresses well with the number of TVs, giving everybody TVs will not bring identical QOL.
Business has to come first but if the plan is to continue to sacrifice them to local social democracy and corruptive practices the businesses won't come. You know, only so many times can you tell a person you are harming them for their own good.
Once (and it won't happen) the businesses come back in the people will want to return to the local core and shorten up the commute... But only after security is improved in those areas.
I think Detroit could come back, as in its doable, I just have no faith that people will get rid of various malfunctional precepts to allow that to happen.
If anything this should remind people and urbanists particularly, a government does not build a city, people do. People are the ones who keep in check to meet relevant needs and their the ones who will build whether its big money (buildings, urban housing) or small money (personal gardens and other micro and self investments). People have to feel it is worth their risk.
The real issue... You can't get around economics as long as you have a free society... People can leave. If you have an unfree society people won't try. Thinking you can milk them for your ideals is a form of slavery. You want them to do the best, leave them alone and let them build society.
In the end, Detroit shows the limits of coercion. That's what the social democracy is about, coercing others to provide for the desired results of a political class. In the end, if you coerce them to do things counter to a functional society, regardless of the morality of the ideal, it falls apart. Want a thriving society? Let people be free and let the pursue.