They're possibly referring to the top and bottom bezel.
The home button has become iconic and I highly doubt Apple will ever get rid of it. And since they insist on keeping the top and bottom bezel the same we end up with a phone that's bigger than competing phones with larger screens.
Might happen when the technology is there to do what they want.
I'm talking about the patent I think was granted or applied for, to do with a Touch ID sensor embedded on the screen.
Once that's doable, and a "clickable" screen (not fully clickable, just a pressure sensitive bit), they might ditch the home button.
Edit:
Found the article for the on-screen fingerprint sensor:
https://www.macrumors.com/2013/11/25/apples-plans-to-enhance-touch-id-with-trackpad-capabilities-and-display-integration-revealed/
Edit:
And pressure sensitive screen stuff:
https://www.macrumors.com/2014/04/03/apple-pressure-sensitive-touch-screens/
https://www.macrumors.com/2014/01/30/pressure-touchscreen-patent/