You could argue that setting up a "binary system" is what Warren, Dearborn, Southfield have been striving for for decades (recall Southfield's motto, "The Center of it All"). "Greater Royal Oak" wouldn't be fundamentally different, just, slightly bigger.
Most of the examples of metropolitan consolidations I know of are city/county mergers, like Louisville, Lexington, and Indianapolis--cities where, generally, you don't have the sheer number and fragmentation of suburban communities that metro Detroit does. Maybe a better example of a "binary system" would be Minneapolis/St. Paul, relative peers in population, and with many more elements of regional governance in place.