—reduced bezels. The iPhone X does not have them. Not really.
The ratio of the screen-width to body-width is 0.88 in the iPhone X. So 88% of the width of the body is covered with screen.
The numbers for the other iPhones:
-SE: 0.85 (85%)
-non-plus: 0.86 (86%)
-plus: 0.87 (87%)
Reduce those bezels, Apple! For real. So that 93% to 95% of the body is covered with screen.
—reduce the roundness of those rounded corners. The body and the screen can have rounded corners without them being quite that rounded. Very rounded corners make a larger part of the screen less useful.
—start from the body of the iPhone SE, and make it slightly wider. Make it as wide as the iPhones before the iPhone 4: 61-62 mm. Along with those reduced bezels, this slightly greater width (around 5%) allows for the 4.7 inch 16:9 non-plus iPhone screen to fit; the 4.7 inch screen is 38% bigger than the 4 inch screen, and has the same proportions. The iPhone SE is tall enough for the taller 4.7 inch screen to fit, and then some. (In fact, proportionally, the iPhone SE is the tallest iPhone Apple ever did: a length-width ratio of 2.11:1) The slight width increase would also bring this 'SE' to the same length-width proportions as the iPhone X and Plus iPhones: 2.03:1.)
(Alternatively, a 16:9 1080p screen could be fit on a slightly wider iPhone SE body if it has the same "Super Retina HD" resolution of 458 ppi of the iPhone X. With those reduced bezels, the width of this iPhone would need to be 63-64 mm. To keep the 2.03:1 proportions of the length and the width of the iPhone X, a width of 64 mm would correspond with a slightly greater length of... 130 mm. (The iPhone SE is 123,8 mm tall).
That's about as much as I'd tolerate seeing this small iPhone get bigger in order to have a much bigger and better screen.
The ratio of the screen-width to body-width is 0.88 in the iPhone X. So 88% of the width of the body is covered with screen.
The numbers for the other iPhones:
-SE: 0.85 (85%)
-non-plus: 0.86 (86%)
-plus: 0.87 (87%)
Reduce those bezels, Apple! For real. So that 93% to 95% of the body is covered with screen.
—reduce the roundness of those rounded corners. The body and the screen can have rounded corners without them being quite that rounded. Very rounded corners make a larger part of the screen less useful.
—start from the body of the iPhone SE, and make it slightly wider. Make it as wide as the iPhones before the iPhone 4: 61-62 mm. Along with those reduced bezels, this slightly greater width (around 5%) allows for the 4.7 inch 16:9 non-plus iPhone screen to fit; the 4.7 inch screen is 38% bigger than the 4 inch screen, and has the same proportions. The iPhone SE is tall enough for the taller 4.7 inch screen to fit, and then some. (In fact, proportionally, the iPhone SE is the tallest iPhone Apple ever did: a length-width ratio of 2.11:1) The slight width increase would also bring this 'SE' to the same length-width proportions as the iPhone X and Plus iPhones: 2.03:1.)
(Alternatively, a 16:9 1080p screen could be fit on a slightly wider iPhone SE body if it has the same "Super Retina HD" resolution of 458 ppi of the iPhone X. With those reduced bezels, the width of this iPhone would need to be 63-64 mm. To keep the 2.03:1 proportions of the length and the width of the iPhone X, a width of 64 mm would correspond with a slightly greater length of... 130 mm. (The iPhone SE is 123,8 mm tall).
That's about as much as I'd tolerate seeing this small iPhone get bigger in order to have a much bigger and better screen.