I don't know, maybe I'm missing something. I have upgraded my iPad Mini 2 from iOS 9 to iOS 10. Official release, not a beta, neither a GM. I don't see any new wallpaper.
Are there any new wallpapers included in iOS 10?
I would assume apple isnt focusing on wallpapers so if you dont see any dont be alarmed since not everyone is looking for wallpapers in new updates and new wall papers might come out in future partial updates.