People who are saying that the GUI should not be changed they have to revise their words. That is like saying Apple should have never updated the OS 9 GUI to OS X as you see in the pictures, because its all about the apps isn't it?
The iOS was created for the iphone, when it was supposed to be just a cell phone. It was so basic that it did not come with an App Store(which came a FULL YEAR after iphone launch) .
Today, it is used on iPads which are supposed to be the "post-pc" era. Where iPads are starting to replace laptops for some people. Remember this was supposed to be a cell phone OS only. It was not supposed to be running Office Apps(something demanded today)
Things change and I believe they need to revamp the whole OS . They just did for the App store and iTunes store which was a great improvement and breath of fresh air, so why not the iOS?
Simple things to consider:
1)Spotlight search should be in the notifications
2) Switching apps should be from notifications too, why to slides, up and down?
3) Commonly accessed controls should be in the notifications like in Android(wifi,bluetooth)
3)Settings of apps should be accessible from within the app not from the general settings
4) new color scheme?
Mobile devices today, are exactly like PCs in the 90s, if its 3 years or older its almost obsolete because technology are advancing so fast in them(we already have games that won't run on ipad 1, only 2.5 years old).
Remember, Windows 3 was only 5 years old when Windows '95 hit the shelf, so why not have the same change with iOS?