During this day I found out that iPhone 6 with 4.7 inch screen he would have one resolution of 1704 x 640 pixels, the resolution being 50% higher than the current one iPhone 5S. An increase in resolution and diagonal is a problem for applications from App Store, these needing an update to be able to be run without problems in these conditions, but even without such a thing, they will still be usable.
Apple will implement in iOS 8 a system called pixel-tripling (3x), practically tripling the basic 580 x 320 pixel resolution of iOS in that 1704 x 960 pixels. If in 2010 the transition from 320 x 480 to 640 x 960 resolution made most applications difficult to use, in the case of tripling the pixels for iPhone 6 change will not have an equally great impact because it will not be as radical.
If in 2010 Apple doubled the resolution of the iPhone 4 compared to the iPhone 3Gs, now we are not talking about a doubling of the resolution iPhone 5S, but about a 50% increase in it. Under these conditions, the resolution of the graphic elements of applications compatible with iPhone 5S it won't be rendered as "dumb/pixelated" on one 4.7 inch screen with a resolution of 1704 x 960 pixels. In the first image of this article, you can see in the upper part a demonstration of the doubling of the iOS resolution, and in the second part a 50% increase, and you can see as clearly as possible that we are not talking about a dramatic change.
In conclusion, yes, a massive update of the applications will be needed to work without problems on iPhone 6 with 4.7 inch screen and resolution 1704 x 640 pixels, but in the absence of updates the applications will be able to be used without problems in any conditions.
