Metro is defined by flat background colors, square corners and no shading. You can have a non-skeumorphic interface without any of those features, and given Apple's history of interface design, it would surprise me if they adopted any of them. Apple loves rounded rectangles, gradient backgrounds and shading to indicate depth, though shine and real-like textures may be on the way out.
Shading and round corners are skeuomorphic, as is indicating depth on a piece of glass.
What Apple loves is irrelevant (if one is willing to ascribe emotional states to corporations). Daimler-Benz loved steering tillers. Ford loved hand throttles.
Think about the way in which the interfaces of automobiles changed over the first forty years as they went from horseless carriages to widespread adoption. That's what we're seeing in computer interfaces.
Rounded corners aren't necessarily skeumorphic; they're a style choice just as rounded cabinets and trim are a (popular) style choice. Likewise, shading and gradients to give an impression of depth and lighting are often used to distinguish items that are clickable or as a separator. These are artistic tools that can be used to various effects, but are not skeumorphic in the sense of trying to imitate a familiar object from everyday life. Virtual representations of objects can be 3D without being skeumorphic; the illusion of depth can be used to convey information.
Skeumorphic features are defined by the fact that they are unnecessary carry-overs from older or different objects. They can be useful and style choices too, but a digital button does not need to indicate depth, whereas a mechanical button does, because it needs to protrude from the surface in order to be pressed.
A mechanical button absolutely does not need to protrude from the surface to be pressed - not only can it start at surface level and be pressed into the device, it can return to starting position and remain flush. Look at most microwaves - totally flat, presses in very slightly, returns to flush. The power button on the mac pro (that neglected tower!) does the same. Also, capacitive buttons exist which, although not strictly mechanical, have a similar behavior.
Protruding buttons are merely a user interface choice. They were never a functional requirement.
Not so slippery. "Tape reels" won't make sense to someone who has never seen a reel to reel. A knobby thing that protrudes, as if you could feel it if you ran your hand over the surface, transcends culture and applies to any normally functioning human being.
The difference between skeumorphism and visual affordance is the difference between "intuitive" and intuitive. One makes a reference to past experience, and is built on natural affordances. The other is not.
That said, I think what you're getting at is it might be impossible to completely eliminate skeumorphism. I agree with that. There's going to be at least a sliver left in almost any interface. That's just one of the byproducts of our having a culture.
An image of a tape reel is to recording audio as an icon of a floppy disk is to saving documents — a lazy visual shortcut, requiring a non-trivial semantic context. What is the percentage of humans alive today who have used a tape reel recorder?
The boundary between affordances and skeuomorphs is perfectly clear. Just ask yourself — does the form of the design element in question follow its function?
>Shading and round corners are skeuomorphic, as is indicating depth on a piece of glass.
And flat background colors represent a uniformly lit smooth surface. I don't think that mimicking some basic material properties is really skeumorphic.
It's more when that's taken to the point of looking/acting like a specific physical object (like Game Center's pool table felt) that I'd apply the term.
Skeuomorphic implies that a design feature is no longer necessary or useful. That's not the case here - you still need visual indicators of the extents of a window, and of what's manipulable versus what's static content, and of what's the currently active or selected object. Apple's current set of visual indicators are obviously not the only option, but if they went to a UI as flat as a typical minimalist web design, usability would suffer.
I don’t think Apple will go that far. I don’t even think they will overtake stock Android when it comes to ditching skeumorphism and removing affordances.
I also don’t think there will be radical changes. Remember how OS X looked before Corinthian leather arrived? That’s what I see more off in the future. Probably with an updated look (like the new iTunes?), but not much more.
If you want to know how that looks on iOS I would maybe look at something like the editing interface of iMovie, Safari, or Mail.
Next version, probably not unless there is the perception of a burning platform.
But over the long haul, I don't see how Apple can stick with an increasingly dated and arbitrary visual paradigm. How many people have actually been around real to real tape decks or owned a leather desk calendar? And as digital devices like smartphones become more ubiquitous, fewer and fewer people will.
We've already seen lots of small changes to take advantage of the extra screen height. Virtually all the iOS built-in apps and many third-party apps have made tweaks. Not just stretching the size of the main area in which you view data or other stuff, but actual interface changes as well.
