I agree with everything said here. The whole concept of the cursor position being related to head movement and to mouse movement at the same time, seems totally illogical. It's a definite spoiler for me.
As for how easy it would be to do implement the option of decoupling head movement to mouse movement, it's hard to say... but it sounds easy enough! I guess it would also require some means to recenter the cursor to where your looking in VR, or you could find yourself searching for where you last left the mouse cursor! Again, it doesn't sound like rocket science.