Most important to any psychedelic trip are set and setting. If you lead a mostly positive life and don't carry emotional baggage, your psychedelic trips should be mostly beautiful and non-threatening. If you have a lot of negative baggage built up or are in an unfamiliar or potentially threatening setting, you are more likely to have a bad trip.
As an experienced ket tripper, I've been in a lot of mindsets going into a trip. I've had beautiful experiences that have changed me for the better, and I've had some trips to hell that have been ugly and scary. The connections to archetypes are always pretty pronounced on this drug. I've never had that happen consistently on other psychedelics like mushies.
I think the researchers should look specifically at 5-MeO-DMT, since that is actually produced by the body and is a potent psychedelic. I believe it has a direct connection to these NDEs.