I have read that some form of four-wheel steering is a feature on a number of production cars, but I haven't been able to find details of those systems.
I'm particularly interested in whether four-wheel steering has ever been applied for non-rotational, crab-like lane-change maneuvers: I.e., instead of having the rear wheels turn in the opposite direction of the front wheels to increase rotation, can any systems turn the rear wheels in the same direction as the front for emergency lane changes?
I imagine the performance advantages of not introducing a rotational moment in the body at high speeds would be substantial: As we approach the limit of a vehicle's handling: conventional steering overloads one tire, whereas a "crab" lane-change evenly loads both outside tires. Not only does the four-wheel maneuver maintain more tire contact for a given rate of change, I think it will execute the maneuver more quickly and in less distance, because it is only trying to translate the car's mass, not also rotate its momentum.
(Another question that remains is how the car would "know" that the commanded turn is a lane-change instead of a turn, unless the driver is given an additional control to command a "translation" instead of a "turn.")