a major part of the issue is UA (and other airline's) reluctance to change the gate for the next flight. Ie, if your plane is going DTW-EWR and then the physical plane is going EWR-MCO and the EWR-MCO flight is scheduled from C85, if they change the gate coming in from DTW to C72, you need to get word to 200 people to go from C85 to C72. As more passengers get comfortable using the app, move away from paper based boarding passes, etc, those gate changes 'could' get a bit easier