Until we can run safe, targeted, empirical experiments around consciousness, we are stuck using noisy outlier cases (like those who have physical brain damage) to extrapolate from, with no control, defined variations, or iterative deductions possible.
Alternatively, if one could quickly design drugs to alter conscious experience in a targeted and safe way, not only would it open up the population of people who could partake in these kinds of experiments (legally of course) but also open the possibility of a new frontier of exploration, with tactical ‘expeditions’ set out by researchers, similar to the astronauts, where there was some risk but the artifact would be validated knowledge about the brain and mind.
In combination with other experimental techniques, one could imagine a whole host of hypotheses which could be rapidly tested in a replicatable way that presently are not possible to do so. For example, the question of if these experiences are completely self-created psychoses, or if the ‘entities’ seen during these experiences have some, if partial, external coupling (even if it is as benign as non-living, static environmental factors), could be readily tested if it were possible for repeated, controlled, experiments to try to falsify various claims.