Here's what I'd love:
1) Mobile wallpapers i.e. vertical-oriented dimensions. I have a Galaxy Note 2 which has a resolution of 720 x 1280 and it's annoying to download widescreen wallpapers, rotate and crop/resize.
2) Mobile app that at the very least can rotate wallpapers according to my Wallhaven favorites, on a schedule of my choosing. Could also be used to easily upload images on the go too, respond to comments etc.