This doesn't really solve the problem, as the whole point to all this is preventing people from catching something and taking it back to infect someone else in their home area.
So, you can let only young, "healthy" people into the park, but then if they catch something, are asymptomatic, and take it to the airport where they infect someone not so young and healthy....or they go back to Nebraska, and infect an older coworker or grandma and grandpa...then that completely defeats the purpose of not letting high risk groups into the parks.
One thing about only letting non high risk people in the parks is....you can't visually see so many high-risk things....asthmatics or diabetics or someone with a history of cancer. Or maybe they are a smoker. And, I'd really hate to be the CM who is put in charge of visually determining who is "too obese" for entry.
Yeah, this is the one that would be a dealbreaker for me. If Disney closed all indoor attractions/shows, they'd be in deep trouble. They might as well just not open if that was the case.