The FDA requirements for the original clinical trial were wild: "...the FDA required them to find a cohort of 300 healthy 18-30 year olds who lived alone, not near a school zone, and had fully removable teeth." I can see why this makes sense, but no wonder they failed at enrolling the cohort.
For FDA, never permitting it is a completely acceptable outcome, and that's why it probably will never be permitted in the US. Unless somebody will find a reason to spend many billions of dollars to make it happen, which I don't foresee happening. I wonder if there's a chance in other countries, or they have their own FDAs?