I agree with much of what you've been saying about the virus, but I think your final two sentences are overly broad. I would agree that in something like a limited run of "Betrayal," chances are very good that most everyone in the audience will have been vaccinated, for a number of reasons.
I don't think there's any way to be so sure about a blockbuster like "Lion King" or 'Wicked." There's no way those shows chug along for decades only on the power of Democratic-leaning people who can read. Tourists file into "Phantom" from buses. Broadway isn't for just one kind of person.