Single-finger swipe from the bottom won't work well, as your fingers hang out down there much too often; you'd be triggering it accidentally all the time. Using

Single-finger swipe from the bottom won't work well, as your fingers hang out down there much too often; you'd be triggering it accidentally all the time. Using the keyboard, for example, would be tedious. If the bottom were a hot zone, it would have to be triggered by multiple fingers, which is awkward on a small phone screen.