Please think of this: the more buttons are replaced by gestures, the more gestures have to be learned, remembered and performed more exactly by the (poor) user. A button on the screen remembers the user for the available options in the current screen.
2nd: this gestures have to be recognized correctly by the OS. It’s boring if the user frequently has to struggle with misinterpreted gestures and have to go back (if possible) and try again.
3rd: There are people who complain about using the phone with one hand is difficult. This problem would become worse if more gestures are necessary to operate the phone.
So I vote against replacing buttons by gestures. I suggest an option in Settings/Gestures: ‘Do you prefer gestures or buttons to control apps’, with 2 options.
This way, both, the gesture fans and the tapping fans could have what they prefer.