Ironically, there's only a concept of "up" because of the very same home button.
If you remove the home button then there is no up and down, since the virtual home button would always rotate to the bottom per gravity.
If you remove the home button then there is no up and down, since the virtual home button would always rotate to the bottom per gravity.
If they could use identical transducers that perform well as both speaker and mic, then I'm sure the remaining buttons could be made virtual as well (full touch-sensitive sidebars maybe?), although personally I like having certain buttons implemented as physical devices.