Let me rephrase what I said before because it came out weird:
Actually in 1999, the MTA-LIRR-Metro North wanted the M7 to be "The Metropolitan/Cosmopolitan Car of the Millennia/21st Century!" They didn't want a third-generation Metropolitan/Cosmopolitan Car with the M1/M3 default chassis blueprint right down to the aerodynamic shape. To me it looked like a M1/M3 car with some changes to the detail such as the leaflet doors, the coupling system, embedded headlights above the cab that were added to the original fleet in the 1990's, and of course all the amenities that a M7/M9 car has. The original concept looked like what a LIRR/Metro-North Car would look like in 1990 if it was 1970 with M1's rolling out already. Something you would see on the Jetsons.
M5 cars were aborted because a car usually fits 100-120 people, but with all the equipment downsized to one car on the underside and with a bathroom, it would cut the capacity in half to 50-60, plus 20 more for standing only in both vestibules.
This station is Babylon, this is the train to Penn Station. Stopping at: Lindenhurst, Copiague, Amityville, Massapequa Park, Massapequa, Seaford, Wantagh, Bellmore, Merrick, Freeport, Baldwin, Rockville Centre, Lynbrook, Valley Stream, Jamaica, Kew Gardens, Forest Hills, Woodside, Penn Station.