Just got through reading the latest UI spotlight over on wow.com, to which I apparently can't link here.
Anyway, the approach highlighted was one of hiding various UI elements when they aren't needed, which is quite different to nUI's approach of putting it all out there all the time. Also, if you're going the "hide stuff until needed" route, it would seem viewports are not needed.
Anyway, I thought I'd start a thread on it, since I kind of like the idea, and wonder what other nUI users think, and whether 6 will let us do this kind of thing.