SDK and other leaks have sort of confirmed that Windows Phone 8.1 will bring custom background for start screen. Now, two more images leak in China and they show how the start screen will actually look with images set as background. As you can see in the above screenshots, it does look good.
You can read our massive changelog for Windows Phone 8.1 for knowing more about the leaked features and changes.
Thanks Xio-Feng for the tip. Cheers!!