One issue that none of the posts in this thread have addressed: the Regional Transit Authority. This is the real game-changer in the Detroit metro area transit scene. Underlying all the financial issues is a deep, long-term city vs. suburbs split. Suburbs are where the money has (mostly) fled since 1967. Many suburban jurisdictions would far prefer to ignore the City of Detroit and make it as difficult as possible for its inhabitants to invade their refuges. That seems to be the underlying reason why Livonia (for example) opted out of the SMART system.
The RTA proposal spearheaded by Gov. Rick Snyder is fundamentally aimed at repairing that split. Snyder realizes that the economic growth of Detroit depends on repairing the divide, and that the prosperity of Michigan as a whole depends on that of its largest metro region. Though a lot of details need to be worked out (and voted on in the State Legislature) having a functional RTA with fund-raising authority is essential regardless of the transit technology being applied.