It already has arrived back when first ls 430 hit the roads...but usually the front collision cars don't have them fixed so a running one is pretty rare...
but I have used that function in a 2000 s500 was pretty scary I had set the distance very near and was playing with the stick to increase the speed had almost hit it to 140 and as the car in front of me moved in the roundabout the merc tried to gain that high speed and in the right moment and someone's kind blessings made me hit the breaks or else might have crossed through the roundabout straight...
This could be very comfortable option for open roads but shouldn't be used in city driving...