You sure about that? I know it is symantics to some but you could take the interurban from Detroit to Pittsburgh, Milwaukee and Louisville. There were actually only a few interurban lines in Detroit Proper.
Check out this paper with a map: https://www.uwgb.edu/dutchs/WestTech/XMODERN2.HTM

What is being described is the DSR.

The biggest issue I see is financing. As you mentioned ROW would be problematic as he would need to negotiate not only with Detroit, but the State and county as well. Once ROW is approved, then you would need to get EPA and FRA for air quality conformity. Even though you would not be using federal funds or this be publicly owned, it will be something that is labelled as 'regionally significant' which will allow the feds to rip your project apart and keep it in review for years.