I think it means grouped app icons will show as a stack on IOS devices (heck, maybe even OS X). Tap the stack, and the stacked icons will expand to show the underlying icons which make up the group. Sort of like Photos on the iPad. An album is represented by a stack of pictures. When you tap the stack, the icons expand outward from the stack, allowing you to choose a particular photo from the album for viewing. Pinch the expanded photos, and they collapse back into the stack. Maybe they are doing the same with groups of apps. This would also potentially allow more apps to be in a group if they make the expanded icons scrollable.
You saw it here first, folks!
You saw it here first, folks!