Indeed, still using this feature at my Nokia E7, but I guess when there is a fingerprint sensor at the side, you will reach it with your tip finger every time when you turn the phone 90° (what you have to do always when wanna to slide it) and at that moment the pin is not needed any more, because when sliding the keyboard, you can already unlock the phone only by holding it in the correct direction and with tip finger on the scanner, am I correct?