They had a hacky demo of this at the Leap booth at Unite in Seattle last week. The Leap Motion was taped to the front of the Oculus, and you could (sort of) interact with a floating sphere. It's a neat idea, but the tech has a long way to go if that demo was anything to go by.
I am excited for the advancement of input relating to VR though.
Given that the dk2 uses IR LEDs as markers to augment it's gyro/accelerometer for position tracking (by imaging them with a webcam pointed at the user). The leap dumping IR out of the front of the visor is going to be problematic, a combination of washing out the DK2 tracking camera and messing with the tracking algorithm by adding extra points.
Though maybe the frequency of the IR LEDs is different enough...
For IR LEDs you have not only the wavelength of light, you also have a repitition rate. Typically you modulate the IR LED with a square-wave in the 10s of kHz; this lets you have a much higher instantaneous power with a much lower average power. If done right, it also means that 2 IRs with a sufficiently different clock-rate will interfere with each other less.
Based on our experience so far with the latest Oculus SDK, mounting a Leap Motion Controller onto a DK2 does not effect positional tracking, since the DK2 was designed to have more LEDs than needed for input experiments such as this.
