Couldn’t find any on the site.
You can find some concept art and screenshots here:
Some good folks over at Reddit have already thrown a few backgrounds/wallpapers together. I won’t presume to tell you which ones to pick, but a search of the Diablo sub-reddit for the phrases ‘background’ or ‘wallpaper’ throws up a few beauties.
I’ve already stolen this one to use for myself:
Thanks for this, will use them
Hey Guys, please check my new 4K Wallpaper, have fun