The game doesn't support one joy - con in horizontal mode. (mygameslounge.com)
And vertical images appear as small versions presented in horizontal mode; RIM said it will add that capability in a future update. (computerworld.com)
Lastly, the other new feature is an orientation lock, which means you can lock the device to either landscape or horizontal mode so you do not accidently mess up your layout as you read, and shift positions. (goodereader.com)