Do we even need an electronic boarding pass? It will not be long before all valid passports are chipped. A security agent or airline staff can just read your passport to verify you are boarding the correct flight. Gate number and flight times often change so it would be unwise to rely on your printed paper for that information. You could be told your seat number by the crew member making the final check at the door of the plane and your initials could be displayed above your sear as a reminder when you near the correct isle.

Also, consider the fact that you have to show the TSA your boarding pass. If you have to unlock your phone for that, they get full access to copy all your data if they decide you look like a terrorist.

Likely not a consideration for most people who don't mind privacy stuff, of course.