From a medical perspective, the question of whether rather than to what degree a patient is conscious has serious ethical/practical importance. Basically, to treat a conscious patient you need his/her consent, for an unconscious one you don't, because you're excused for not getting it. So that variable, in a binary sense, is something every medical researcher is very aware of.
I agree that it is not ideal as a measure of how well someone is able to integrate information into his/her subjective worldmap (or however you want to define consciousness), but it is very available.
Basically, to treat a conscious patient you need his/her consent, for an unconscious one you don't, because you're excused for not getting it.
That's really stretching the word "basically". If a patient is unconscious and there's an urgent issue that will cause serious injury if not addressed and it can't wait until the patient regains consciousness and you did not have an opportunity to get consent while the patient was conscious, then you have an argument for not getting consent, but you can't go around treating unconscious patients willy-nilly.
This paper, or more often the New Scientist's exposition of it is being discussed online and is rather topical here. In a nutshell, stimulating one small but central area of the brain reversibly rendered one epilepsia patient unconscious without disrupting wakefulness. Impressively, this phenomenon has apparently been hypothesized before, just never tested (because it's hard and usually unethical). A quote from the New Scientist article (emphasis mine):
One electrode was positioned next to the claustrum, an area that had never been stimulated before.
When the team zapped the area with high frequency electrical impulses, the woman lost consciousness. She stopped reading and stared blankly into space, she didn't respond to auditory or visual commands and her breathing slowed. As soon as the stimulation stopped, she immediately regained consciousness with no memory of the event. The same thing happened every time the area was stimulated during two days of experiments (Epilepsy and Behavior, doi.org/tgn).
To confirm that they were affecting the woman's consciousness rather than just her ability to speak or move, the team asked her to repeat the word "house" or snap her fingers before the stimulation began. If the stimulation was disrupting a brain region responsible for movement or language she would have stopped moving or talking almost immediately. Instead, she gradually spoke more quietly or moved less and less until she drifted into unconsciousness. Since there was no sign of epileptic brain activity during or after the stimulation, the team is sure that it wasn't a side effect of a seizure.
If confirmed, this hints at several interesting points. For example, a complex enough brain is not sufficient for consciousness, a sort-of command and control structure is required, as well, even if relatively small. A low-consciousness state of late-stage dementia sufferers might be due to the damage specifically to the claustrum area, not just the overall brain deterioration. The researchers speculates that stimulating the area in vegetative-state patients might help "push them out of this state". From an AI research perspective, understanding the difference between wakefulness and consciousness might be interesting, too.