Now that we know what virtual objects are about, we can move to a design scheme that's made for virtual objects.
I inherently don't like the phrase 'Flat Design' - there is so much more to this.
in many of the comparison screenshots of ios 6vs7 it looks like they just switched from textured background to a solid background, and left the workflow the same. Not an eschewing of skeuomorphism but a change in visual style.
I have a feeling that in a few decades we'll be looking back on the 2010s like we do the 80s and 70s, and "flat design" would be one of the trends that mark this decade.
Sku was teaching designers to fake dimension by hand, flat will aid them to getting to the point of texturing real 3D objects. And if you think iOS7 doesn't still use 3D space to make skumorphic metaphors you haven't looked at Safari' tabs yet.