Oddly, Instant Digital for some reason replied to discussion about the photo they posted by saying it depicted only the flood illuminator on the left, connected to the other components via a ribbon cable, and the MacRumors article took their word for it. But clearly the large part on the left side of that ribbon cable was the IR camera, with the flood illuminator as part of that component, visible as two small pins. The IR camera's lens looks a little cloudy because of the coatings on its surface, to allow only IR light to pass through, and that's what was shown on the component on the left in that photo. The selfie camera lens was shown at the right end of that ribbon cable, and to the immediate left of that lens was the dot projector, identifiable by its slightly fuzzy, flat appearance, rather than a lens.
The IR camera seems to be easier to move under the display since it doesn't need to see the dots with quite the exact precision as the dot projector needs to emit them. The dot projector is actually the tougher part to place under the display, since with current display technology, the display pixels get in the way of the 30,000 dots emitted by the projector, and this messes with the precise angles that each beam needs to be emitted at. The Face ID hardware/software expects all of those dots to be emitted at a certain angle, and if those beams get diffused by the display layer, they no longer work accurately. There's only one infrared LED in the dot projector, and it gets split into 30,000 beams by a very precise diffraction optical element on the projector's surface, and if there was a display layer above it, that would act as another, undesired diffraction layer. So display technology and the IR dot projector will both probably need to be redesigned to move the dot projector under the display, so they can work together to get the beams to reach the user's face with the same precision as with the current system.