New Study Using Hydroxychloroquine Shows Zinc Is The Key, page-5

https://patents.google.com/patent/JP2005145864A/en

Here is a patent from 2003 for coronavirus disinfectant spray using hinokitiol, presumably an inspiration for the current endeavor.

One of the issues they discuss is the need to mask the strong odor of hinokitiol. If it smells that bad, I imagine the taste could make people gag.

The patent is withdrawn... Does this mean it is unprotected?

Another potential issue with putting this stuff in a mouth spray is toxicity. The lack of regulation around the ingredient has more to do with lack of data than confirmation of safety:

https://pubmed.ncbi.nlm.nih.gov/14871589/

Why don't we develop a surface or hand sanitizer in tandem with the oral spray? Seems like the path of least resistance, in case there are issues with the latter.