I have uploaded new unity-settings-daemon and unity-control-center in the maintainers ppa which fixed the issue of crashing u-s-d due to missing/dropped gsettings background schema. It will also pull new version of gsettings-ubuntu-schema. You can help testing by installing those packages from the ppa until they land on universe.
Changing wallpaper now works as expected. In the absense of nemo-desktop u-s-d changes the wallpaper both in desktop and lockscreen.
Control center now correctly reflects Ubuntu version… I will update greeter version later in another merge.
Update: u-s-d and u-c-c has already been landed (Thanks to @seb128 ). The ppa is no longer needed.