[Tracker]

I can imagine Oculus Rift, or Head-Mounted Displays (I didn't know HMD stands for that) being used in FPSes like Full Spectrum Warrior, where aiming is more-or-less separate from looking around. So you could still use your mouse to aim, you would move a crosshair across your vision.
Well, it is only natural that this kind of VR technology would be more than suitable for simulators - the level of immersion is close to real in racing games where you have a steering wheel and pedals like in real cars, especially with force feedback supporting wheels.
Imagine sitting in an AH-64 Apache attack helicopter simulator, firing at targets with the Integrated Helmet and Display Sighting System (IHADSS) - a system which lets you target stuff by looking at them!