Setting aside the Launcher replacement, the most technically surprising aspect of this demo was the messaging app: it showed avatars and a messaging window hovering above the currently-focused app.

As far as I know, this isn't possible on stock Android. You can make a non-fullscreen window, but you can't continue to interact with the layer behind it.

This may be the motivation for the "set of OEM guidelines" Mark very casually mentioned. I wonder what other enhancements they call for..