That's the point. They haven't figured out how to do it safely yet. The video shows that. If you have ideas please share them. Disney clearly could use them.
An additional layer of safety control that I would suggest (beyond what Disney is testing in China) is to use the Fastpass system to control the visitor experience throughout the day. There are no more stand-by line's all attractions are available through the Fastpass system only. You get a Fastpass for all (or most every) attraction that is deemed safe to open.
What I am thinking is removing the current Fastpass system as we know it. In it's place, Disney fully plans each guest's day to control the flow of people moving about the park. I am thinking that Disney assigns guests into packs, let's say 10 packs. Each pack is assigned an itinerary for the day that includes each open attractions, breaks, meals, shopping and a small amount of free time. Attractions are assigned to you in a specific order with tighter windows of time to try to restrict the amount of free movement throughout the park. The order of events is different for each pack.
So let's say pack 2 starts their day in Tomorrowland. Everyone in that pack is assigned either Peoplemover, Buzz or Speedway (assuming Space isn't immediately open). Everyone in the pack is given one of these attractions for their first assignment of the day at a scheduled time. Then, once they check in, they have 20-30 minutes to get through the attraction and move on to their next assigned attraction (one of the other three attractions for that pack). So if I am given Speedway, check in at 8:30 (my given time) and at 9:00 I have to check in at my next specified attraction, Buzz. Then my next assigned attraction is Peoplemover at 9:30. Other people in my pack will be assigned a different experience order in our area (some will start at Buzz and some will start at Peoplemover.
Everyone in the pack gets access via an assigned time in the Fastpass system, to each of these attractions. Once that pack has been given the opportunity to visit each of these attractions, the while pack moves to the next assigned land which is also structured in this manner. Fastpass gives you the itinerary for the entire day.
Control the flow as best as you can, so only one pack is in an area (or two packs is the land is large and spread out, like Fantasy land). Keep the timing tight so people don't wander too far. Allow time for bathroom, some photo ops and snacks.
The aim is to keep packs together as best as you can manage for vector tracing.
Load the back of the park first with the groups first assigned to back of park areas. Guests are given windows to enter and exit the park. This plan controls movement and reduces the number of people crossing your path at a given time. Use the hub/spoke design to your advantage where possible.
Some people will wander, of coarse. Some people will skip attractions. You control as many as possible in the best manner that you have available. It isn't perfect but the technology is already in place. They just need to put thought into breaking up the group into packs and designing as flow of experiences to occupy and entertain.