If one were to take a single-speed flip-flop hub, and fit two identical freewheels, and couple them to two identical chainrings (i.e. two drive-side cranks, one on each side of the bike), you would have the world's heaviest and least efficient fixed-gear drivetrain. One freewheel coasts while the other drives. (The left-hand pedal would have to be fitted with a right-handed axle, and thread-lock used to prevent it unscrewing due to precession.)

Why anybody would want to do it is beyond me, but I am certain that this would work.

Now, bear with me here...

What if one were to do the same thing, but with a slightly larger chainring on the drive side, and a slightly larger freewheel on the non-drive side? (Obviously magic ratios would have to be selected for identical chain lengths.)

Would this provide a long gear for high top speed, yet provide a shorter gear for less strenuous leg-braking? Or would the freewheels somehow skip and bind?