And my original thought was professors at universities when I saw a concern on the news about fall semester and wearing masks at lectures. It’s not a novel idea since there is a patent from 2002.
I did think it might be good for stage, but the responses about large breathes for singing is of course valid point even for no dance shows.
Mask or no mask really doesn’t address the issue of cast working closely together for hours a day for months off stage. It’s really impossible to keep cast and crew safe unless quarantine everyone for run of show. And that doesn’t seem to be working for sports teams.