That's already been release since the previous version via the traffic aware cruise control and emergency braking.
Specifically, the Model S locks onto the car in front of you and matches its speed, maintaining a certain number of car lengths behind it (which you can set). When the car changes lanes, your Model S speeds up a bit to fill the gap, and when a car cuts into the lane, the Model S slows down (although this one is a bit scary). If the car in front comes to a complete stop, the Model S also smoothly slows down into a complete stop.
This is correct. My Model S will fully come to a complete stop on the highway and will alert me if I'm approaching a vehicle too quickly and it senses a risk of collision. I've had the car save me from an accident at least once by applying the brake for me.
My wife's 2015 Mazda 3 has this feature as well although for some reason, it doesn't come to a complete stop. When needing to completely stop due to a car in front, it drops down to 2-3 MPH then beeps to let you know you're on your own for the last bit.
In the forums there's always the guy that says we should "drive better" instead. With that logic, there's little use for safety features at all.