(Update 03-05-2019, almost 5 years since original post) I did something similar for iPhone X, XR, XS screen size. Basically I stretched the Default-568h@2x.png to Default-375w-812h@3x.png and added that in the “launch image”. I also noticed the some of the nib files have the wrong constraints for label, textfield and button. I made some simple changes so that the top and bottom portions stick. Last but not least, the constraints and the size of google admob banner ads needed similar work: I did the needful and checked those changes worked both for iPhone SE and iPhone X.
I don’t have iPhone X (XR or XS). My first impression they are much longer than the SE I have.
(Original 04-13-2014) I found some iPhone apps are still not updated to take advantage the iPhone 5 screen size (4 inch vs. iPhone 4/4s 3.5 inch). I think in many cases the owner of the apps may not have time or the developers don’t know how to stretch the screen. This is a quite common problem. The solution is also fairly straightforward. We only need the stretched version of the screenshot, and name it as Default-568h@2x.png (exactly like this). But to get this all started, you might want to use this blank png file, something like this:
Add this file to the Xcode project, and run the simulator. Screen capture the first screen and edit it to make sure it’s 640×1136, and name it as the file name above. This way the app will both have a good launch screen and stretched screen for iPhone 5/5s
(Update 04-20-14) I found something more interesting. When I tried to add auto layout for the nib (xib) file created in Xcode 3.x, it basically give me a blanket (black) screen. So basically we can not reuse those old nibs for auto layout.