Actually thinking about it...if Apple did a force touch to wake it could be pretty awesome. So a light press would turn on the screen on low brightness, slowly building up as you increase pressure. Let go and it turns off, commit to the press and you are in.
Agreed. My LG G2 had that, and it was absolutely fantastic; but no phone since then has had double tap to turn off, only on.
I guess they're worried about false positives. But LG solved this by only allowing double tap to turn off from any of the default apps (home screen, notifications, settings, etc). You had to quit out of third party apps to turn it off that way.