For people who plan Disney trips, living by an app is already the name of the game.
I'm curious how reduced capacity the park will be or what they will to to increase capacity. For the diehards like us, we'll go in some form or fashion but not everyone is going to make the trek. Hopefully with lower attendance and everyone being forced to use the app, the servers will hold steady and stays solid once people book this house order or however it will work.
Assuming this is using similar tech based off its virtual line system for the ride and Volcano Bay, you'll probably get a barcode or QR code to validate your reservation to be let into the queue and if it works like Fast and Furious or Jimmy Fallon, I'd take a screenshot on my phone as soon as it appears on my phone so I have a record of it in case the app crashes while pulling it up again.