When you have a platform like iOS that is very app-centric, a Home screen UI with rows and rows of apps makes zero sense. It's too ugly and confusing and more important, it's boring. That's why Windows is superior with their live tiles. When you have a company like Microsoft that makes a rich and diverse set of first-party apps from word processing to music editing to film editing apps as well as having a very robust third-party developer community, a hub system of tiles makes a lot more sense than rows and rows of app icons.
Widget support is paramount. Giant clock and weather widget on the Home screen. Also, LIVE WALLPAPER. Something very cool and animated. Anything to make iOS less boring. I think it'd be very fun if icons were floating on the Home screen as if floating on water and the user has to hunt and peck the icons. Now THAT'S fun.
Apple also needs to provide a REAL file system. Too many users are frustrated that they can't access a file system on their phones. Last night my grandmother was using her iPad and said: "Where's the damn Finder?" And I said: "Grandma, iOS doesn't have a Finder, you know that." Frustrating.
I would love to see more productivity-focused features from Apple, especially in the form of first-party apps. Go to the App Store and look at Apple's portfolio. Literally nothing. Useless apps no one wants or needs. Health? Really, Apple? Who the hell needs Health? We need real apps and real features for real people to get real work done.
Oh, and themes! Frankly, Apple should forfeit UI over to the users. That's one reason why MySpace was so hugely popular—users could decorate their own profiles! San Francisco font is ugly and not very fun. And the icons are very ugly.