The problem is well known, apple dealt with it when they went from 3.5 to 4 inches..The sollutions of getting to a 4.5 or 5" form factor are also well known..Their are multiple paths apple can take to that end..3x or 4x would mean extremely high ppi LCD screens..or switching over to high ppi AMOLED screens..Apple is likely going to stick to LCD..How they acheive that could be simply bumping up, or asking developers to re-do apps.
http://www.imore.com/did-you-hear-one-about-iphone-4x-super-retina-display
http://www.imore.com/apple-ios-apps-updated-compatibility-iphone-6-wait-what
Again missing the point. How iOS deals with objects on the screen is different than how Android does. You keep talking about the tech. And I am telling you - there's a fundamental difference in how the OS operates - regardless of screen size.