I'm MORE interested in the core API's, structure, and core of what we know to be iOS in current form to be overhauled!
I think the core OS is fine (Core Data, Core Video, Core Animation, Core Audio, etc).
iOS 5 had more core OS "developer" features than any previous iOS. iOS 6 didn't seem to contain much of either (consumer or developer), which makes you wonder wtf the iOS team was doing this year.
The springboard is where Apple needs to focus their attention. While easy to use, it's become a relic compared to other mobile operating systems.
I feel like Forstall (and likely others) have been holding the springboard back for fear it won't be user friendly if it contains live tiles, widgets, etc.
The springboard is the face of iOS. It needs an overhaul.
My suggestions? Get rid of the multitasking bar. Add expose. Add dashboard widgets. Add stacks and animated icons. Notification Center needs to be reorganized and more useful (I know a lot of iPhone users that don't even know it exists). Kill the linen background.
By the way, with all the Forstall bashing (and I've joined in too), he should get a lot of credit for the creation of both Mac OS X and iOS. He even was a lead designer on the the Aqua interface.
Regarding Aqua, I do like what has happened with Aqua over the years. With Leopard, it became much more mature and modern (and Forstall reportedly managed that Leopard team). I would love to see that come to iOS.
I feel like iOS in where Mac OS X was at 10.3 or 10.4 and needs a 10.5/10.6 to push it on into the next five years.