Also, is there any reason a phone with a mechanical button cannot do this? Obviously the iPhone 7 doesn't wait for a second click before animating, but why is that a "7 only" feature?
Could they not start the animation immediately on the first click on a 6s and then interrupt the animation if a second click is entered mid-way through?
You can't double press as fast on the 6s since you are physically pushing a button down, so it would be harder to double press in time to interrupt the animation and get to the app switcher.