The question (for infectious disease experts) is does WDW fall into the category of a large gathering? If it does, then I would think malls, destination shopping centers, mass transit and in some locations would as well.
While there is certainly a large crowd in each park, they are not really confined together. The confinement happens in the queue and to some extent on the ride. Is the number of people in the queues and the way they are spread considered a large gathering? Again, more of a question for infectious disease experts.
Basically, if the risk of transmission at the parks is similar to the risk of transmission in those other locations that I mentioned it would logically follow that if you close WDW parks, you must also close those other places.
I would assume that other than touching surfaces and not washing hands, I would think the queues have the highest risk of transmission. My suggestion would be to go completely to virtual queues done in a way that the guest will flow and not bottleneck. Any ride shut downs would require clearing the queue. The technology to modify the FP+ system to do this has to exist even if it takes a week or two to implement. Even re-use the boarding group software with some modifications to join throughout the day for normal rides.