Even if the GUI would be perfect and much better than android or iOS (which I greatly doubt, simply because of the man hours that went into those projects) there are two big things missing. An ecosystem of apps+apis and IMO even more important: sandboxing.
Applications having access to basically everything just doesn't fit anymore today. It would have made much more sense to concentrate on these technologies and get sandboxing on the desktop, as all the competitors are also still struggling with that.