Only thing to add is that this is only available 24 hours prior to the flight. Not sure how far in advance the person that asked was hoping to see it.
Also the app only shows people who have checked in .... so there might be 30 people on the wait list, but if only 2 of them have checked in at that point, you'll only see the 2.
All of that means the app is most useful in the last hour or so before departure. Enough time to let you know if you should grab some extra food & drink in the lounge or not ... and perhaps help to manage your expectations just before the upgrades process.