The 4.7 Moto X is almost exactly a quarter-inch wider than the iPhone 5s. I would expect Apple to do something similar by eliminating much of the bezel on the sides. Which means a 4.7" iPhone will be bigger but not by as much as the display size difference suggests.
However the physical form factor is only one part of it. A bigger display with smaller bezel still makes one-hand use more difficult, and having less bezel sometimes makes it even more so because your palm pad may tough the screen.
Having used a wide range of smartphones from 2.8" to 6.4", my favorite form factor is the latest iPod Touch and the favorite screen size is 3.8" which is still found in some Windows Phones. Even Apple's 4" screen is slightly too big for comfortable one hand usage even though I have a fairly large hand.
A 4.7" iPhone will be nice to look at and won't be that much bigger than the current iPhones but it'll certainly be a sizeable downgrade in one-hand usage. It's unlikely Apple will produce another 3.5" or 4" flagship spec device and I'll be unhappy but it seems there isn't that many small display smartphone enthusiasts out there