Not very interesting in my opinion. If it sounds interesting it is because people hear and/or are experienced about the effects of dmt in the somewhat non-canonical situation where one person is administered an admittedly massive (or non-physiological, beyond the endogenous levels) dose.

Even though dmt freely passes the blood-bran barrier it does not provide any information about dmt's spectacular effects when smoked or IV'ed. It could just the same case as with many hormones in the body, vis:

They get to the brain and "report" the status of many body organs. As an example testosterone from the testis, travels to the brain, crosses the blood brain barrier and reaches the pituitary gland and hypothalamus to give the message: "Oh, we are producing too much sperm, we need to slow down a bit" or "we do not produce that much sperm, we need to boost the situation a bit"

In a similar manner, dmt produced peripherally may cross the blood-brain barrier just to report on physiological processes. Its actual role in the body may not have anything to do with "reality", "conciousness" and the rest of the lot.

How about this theory:

DMT is used in the wake/sleep regulation of the whole body. Processes like blood flow, blood production, breathing, liver metabolism operate differently when we are asleep. And they have to operate differently, simply to orchestrate the whole "sleeping state" that the body has assumed. DMT is produced by the peripheeral organs, telling the brain: "yeah, the organs are behaving the way they should during this sleeping process"