Very important to note that silica can not be forcefully coughed out, even from a human. That's the real inherent risk, but as I mentioned before you can purchase topical application forms that are pre-wetted.Note: all five or so papers I could ever find (that were in English or had translations provided) on DE and birds point to it being significantly effective (not the same thing as functionally effective, mind) at reducing the severity of infestation by Ascaris species as measured by the number of eggs recovered from feces.
It's not exactly safe to say it works—especially not against all worms—but it would be uninformed to call it ineffective.
Definitely more research required. I won't be giving it to my quail, but I won't tell people not to use it except to warn them away from giving birds an opportunity to breathe it in. Birds lack a diaphragm so can't cough to forcefully clear their airway, and their air sacs are so delicate that diatom shells are very likely to irritate or worse.
I would love to see more health management studies regarding quail in general. Most are focused on incubation practices and maximizing fertility. Hopefully as the industry expands we'll see more expansion on topics. Definitely need some welfare inclusion, the current farming practices that are allowed are just outrageous.