This sounds great but I just can't get by the oxygen deprivation and potential harm to your brain. Not to mention the hypercapnia induced tetany is very uncomfortable and seems a clear signal from the body that "this isn't good!".
[As part of a psychedelic retreat we did breathwork the day before the trip to "open the mind". I faked it because I was worried about the above unanswered questions I had. I still had a great trip and feel no need for another one or similar (ie. via breathwork) to this day. :) ]
In response to this there is vasoconstriction of the cerebral vasculature. No one knows if mild damage is being done to the brain from this.
Somewhat related (not exact same mechanism, but similar), there is evidence elite free-divers are harming their brains [1]. It is easy enough to find literature about the appearance of SB100 protein with too long apnea training (eg. [2]).
However, breath-holding/apnea is not the same as breathwork. The fact of the matter is, there will be no definitive proof one way or the other until someone directly probes cerebral O2 levels for an acute and chronic intervention of breathwork. Again, as someone who has indeed done psychedelics and meditates, I am open to alternative modalities, but I will personally wait for the science over anecdotes.
At least I appreciate they have the decency to not call it "higher states of consciousness". Altered is what they are, altered almost to the point of losing it, but definitely not higher - at least for my understanding where "higher" would mean some added capabilities not attained otherwise.
I think I recall reading a paper a while back on free divers that showed there was damage being done to the brain even though it wasn't immediately apparent. Similar to how lots of small brain impacts add up in football players.
I'm almost certain any amount of oxygen deprivation is damaging to the brain. If there were studies that showed conclusions to the contrary, I'd be very curious to read them.
[As part of a psychedelic retreat we did breathwork the day before the trip to "open the mind". I faked it because I was worried about the above unanswered questions I had. I still had a great trip and feel no need for another one or similar (ie. via breathwork) to this day. :) ]