Not that it comes as a huge surprise, as many Android overlays are already offering this option, but the Galaxy S8 may have on-screen navigational buttons whose arrangement order can be modified.
As you can see from the leaked videos of the alleged Galaxy S8 in a working state, the phone can have the back key at different places, which is pretty awesome, as there is nothing more annoying than having to stretch not only all the way down on a big screen phone each time you want to go back a step, but also all the way to the opposing side of the screen.
This way lefties will be pleased, too, and who knows what other arrangements could be there. Huawei's Emotion UI, for instance, not only allows you to rearrange the navigational strip buttons as you please, but also has a key for pulling down the notification shade. Good times and good riddance, fixed physical home key and capacitive navigation buttons.