http://www.xboxmad.netTalking with TiC Podcast, Phil Spencer confirmed that the Xbox One will be receiving custom backgrounds, themes and screenshot functionality in the future.
In response to the question about the Xbox One UI, Phil Spencer elaborated that they are working on including the features in the monthly updates, owing to development time and priorities.
"You will see , I'll announce it here, I was told themes and background pics are something that we are working on, and screen shots!"