Dhatu-vibhanga sutta question?
If you look at original Pali, what they translated as "consciousness" is actually "vijnana" - (discriminative) experience. 

The point of the sutta is, as you meditatively investigate what seems to be your "I", you progressively exclude all physical elements as obviously not "I", until you are left with just experience itself. Then you investigate that experience and realize that it depends on the sensory input, which depends on attention.

When you don't pay attention to any sensory input, experience stops. What's left is called "equanimity" ("upekkha"), characterized as "luminous" or "radiant" ("pabhassara"). See Pabhassara Sutta for the canonical reference to "luminous mind".

Then Buddha explains that although this equanimity can be shaped into any other meditative state, including the formless jhanas, the meditator understands that any such state would be contrived and conditioned and therefore finite and prone to suffering.

This realization leads to letting go of desire to attain any state different from what is presently unfolding. The resulting state is pure suchness providing no basis for suffering to arise. The meditator realizes that this indeed is the culmination of the path, "the knowledge of the ending of suffering". 



So, the "experience" is not analyzed as internal and external because we are talking about meditator's own experience as he tries to find who he is by separating from everything that is conditioned and unreliable. Experience (vijnana) itself is conditioned on sensory input and is therefore unreliable, not suitable to be called "I" or to be our basis for eternal happiness. Which leaves us with nothing to rely on, nothing to stand on - and this final realization being the only unshakable truth, acceptance of which gives unconditional freedom from any mismatch of expectations, - is the very Nirvana the Buddha is leading us to.