I seriously doubt this will be used for gesture controls. This gives Apple the silicon to build smarter devices that can be made "aware" of your presence and activities and act accordingly. They bought a facial recognition company a couple of years ago. Combine that with this hardware and you have a technology that not only knows if and when you enter an area, it can also "see" who you are.
I believe this is a logical step in Apple's efforts at making their products more aware of the actual person using it and the environment surrounding it. It sounds a little creepy, but this will ultimately lead to truly "smart" products.
Looks like the PrimeSense acquisition may be more about Maps than anything else.