Additional start screen backgrounds for Surface RT?

Anyone have any idea on what the potential is for more start screen backgrounds? I know Build is going on and there may be some discussion going on there, but I have not been able to find anything through my Google / Bing searches.

I think it would be great is MS released an App for users to submit their own Start screen designs. I like a lot of the ones that are stock, but not all of them and I would appreciate a greater variety.