Negative for the sake of negative? Didn't you read? VATS is a broken system, it gives the player a bunch of free actions with little actual consequence for using it. It shouldn't be there, if yo uare turning Fallout into a shooter then make it a shooter, the aiming system in the first 2 Fallouts was an abstraction for aiming carefully, i.e. of what you would be doing while just shooting with the mouse. I rather have no pseudo turn based mechanics at all if they are as poorly desined as VATS. Project Nevada actually has a better alternative to the AP system the FPS Fallouts have by making certain special actions (Sprinting and tackling) and Bullet time consume AP while active. I would say maybe have special attacks with weapons that consume AP so the Ap bar would work as a sort of cool down and you would get access to regular attacks when out of AP.