I would image that they are not be use because they could not provide the required pressure needed to keep the air way open. However, it would be awesome if they could figure out how to get it to work.

They are not used because they do not fix the problem, which is air getting into the lungs.
Questions of humidification are irrelevant.

*PAP works as it pressurises the throat to open it up enough to allow air in.

I found the article interesting because it weighed the pros and cons of the effectiveness of the cannula vs. cpap in terms of long term benefits as they are affected by compliance.

The way I understood the article, it seems that they did establish that the CPAP was more effective in keeping airways open than the cannula. But then because the cannula did still show significant benefits, they suggested the possibility that the relative comfort of the cannula might promote more compliance.

I would imagine that for someone who has a primary issue of compliance due to discomfort might benefit better overall. Or maybe it could be used to help transition someone into full compliance to a cpap. It took me three years to really start using my cpap regularly. I still skip at least a night a week these days. If the cannula does have appreciable benefits, I wish I would have had that choice when I started mt therapy.
MC