New Xbox Experience rolls out later this year will be rendered useless with the switch to a different UI. The answer's a welcome one: they'll work just fine with the new Apple TV-esque interface.
To (literally) illustrate the point, Major Nelson uploaded images of the NXE with an existing theme applied to his flickr gallery. It isn't explicitly stated in the accompanying captions, but we'd venture a guess that the background image will change as you page through the new category "frames." With this mystery solved, you can now go back to complaining about all of the things you actually wasted money on.