I don't see Apple changing the bezels much as that has been the iconic part which makes the iPhone recognizable, and they haven't changed since the original iPhone. They could possibly shave a couple millimeters off the top and bottom of the bezels, but it might end up looking too much like a Samsung at that point.
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Though highly unlikely for the 7 I think once apple figures out how to execute a buttonless bezel less front without negating the Touch ID function they will. The same way they figured out how to make it normal to not have a keyboard/dial pad.
I can just imagine the unibody design of the 6 with top to bottom screen and gesture centric controls maybe using some of the technology used in the apple watch. Maybe with Touch ID built into the actual frame of the phone instead of the screen so that just picking it up verifies your ID.
*DREAMING*
I think the 4.7" and the 5.5" is as high Apple can go. Anything over 5.5" would just be too big. For me the 5.1" is the sweet spot for me (having owned a S5).
Im thinking that there is no way the 7 will get any bigger htan 4.7
Ths iP6+ is as big as I need it to be. I'd say any larger would basically be an iPad mini.