Opening too early will be a catastrophe for Broadway. If Broadway shows open in September, and then have to shutter because of low attendance or Covid problems with the cast and crew, it's hard to imagine what will reopen them.
I've been criticized for being too negative on this subject, with people saying, "You're too negative, you just don't want Broadway to reopen." For what it's worth, my entire income is based on royalties from Broadway shows and touring companies. This shutdown has been a disaster for me financially. But opening too soon will, in my opinion, cause irreparable damage to the institution.
At the time the reopenings were announced, it truly looked like the Covid crisis was over for the vaccinated. It sure doesn't look like that now.