The word on the street is Apple are already testing iOS
6 7 so instead of speculating the features here are my top wanted features (iPhone edition) :
1) People Center/ Contacts/ Accounts: WP7 started it, Android copied it and now is the perfect time for a revamp on iOS. It's simple a contact app that lets you sync with other services such as google and facebook through the app instead of setting up Exchange. Features should also include unification (of services) such as combining iCloud contacts with google/facebook/twitter/linkedin etc and storing all that information in one place to view. This should also pull in status updates and contact logs from various services for a person in one tab. Now if we are really dreaming then imagine all the accounts automatically synced with Email, iMessages and Calender.
2) Notification Center Widgets: The weather widget in the notification center looks beautiful but below it is just wasted space, not many people use the stock widget so why not release an API so devs can get into the action Apple can even even link with other default apps such as quick contacts, or settings.
3) OS Aware Siri: It's simple, make Siri do OS level work "Hey Siri turn on bluetooth"
4) Revamp Multitasking Interface: So much space and information is wasted while switching between Apps, why not use an interface similar to Safari's tab switching or even the iPods cover flow.
5) iPhone Gestures: If pulling down from the top opens notification center, then swiping up from the bottom should open multitasking. If multitasking interface is updated then swiping up or down should close the App.
6) Launchpad for iOS: OSX does a great job of storing all your apps in launchpad, so apps that are not frequently used can be stored there and launched anytime. iOS does the opposite, every app is in your face whether you use it or not, creating a clustered homescreen. Going forward it makes perfect sense for iPhone or iPad to have a launchpad of it's own.
7) New YouTube App: Google has changed the layout of YouTube for the better, yet the App for iOS has been basic since it's release and is very sluggish while playing video. The UI should be updated and performance boost is needed, after all what good are "4G" and "WiFi" speeds if they can't play videos properly.
Feel free to add suggestions