I think one of the biggest challenges is fitness centers. By now a lot of people saw that study where one asymptomatic person sitting by an AC vent in a Hong Kong restaurant infected 10 other people downwind of the vent, many of which were well beyond 6 feet. Fitness centers seem ripe for this kind of spread with the fans, the AC pumping, and people panting as they work out. I wonder if people will work out in masks, that would certainly help.