I’ve never understood why there’s a fuss about default wallpaper. It ships with a dozen options and you can obviously install your own. I guess it’s the opportunity for a news story and a sign that things have reached a certain level of development and are getting close to release.
Personally, I saw the item on installing your own dynamic wallpaper at omglinux.com/dynamic-wallpapers-for-gnome-desktop…, followed the instructions on github and set up a lovely time-of-day based wallpaper based on the game Firewatch (github.com/manishprivet/dynamic-gnome-wallpapers#…) - I love all the sunrise/sunset options there but if you’ve played Firewatch then this one might speak to you :)