The M1 Rail project has been in the urban mass transit imagination since at least 1979. This map comes from a joint report led by the Southeastern Michigan Transportation Authority (SEMTA), from which SMART would form in future years, and the USDOT Urban Mass Transportation Administration (UMTA).
The report also explored the Downtown People Mover (DPM) option, which seems to be the only project option that was funded.
I was fascinated to see that this plan called for the M1 light rail to be subsurface (subway) from Jefferson Ave to Grand Boulevard and then aerial, like the People Mover, from Grand Blvd. to McNichols before functioning at-grade at the street level.