It's somewhat hard to see on the video but if you are talking axial play as in the side of the screen facing the keyboard tilting up and away from the keyboard while the opposing side goes down... It is indeed necessary for the type of slider to work and the spring force has to be somewhat relaxed at the outer positions of the opening/closing movement to allow it to be possible to comfortably opened and closed.

Like if you press the top of the screen towards you (from landscape point of view), the bottom side of the screen should move up from the keyboard as part of the closing motion, thus rotating slightly. But if not applying any pressure in that direction, it should gently be spring loaded against the device, if it is loose and rattles just by moving the device I guess that'd indicate something wrong. At least that's how I think it works (edit: so tell if i am wrong chen / actual pro1 owners ).