I have built a new ISO and updated it from the Dec 21 image. When I removed gnome-shell it pulled all ubiquity files. I finished the build and now the USB boots right into live-session with no options to install.
This is stock ubuntu only . No redshift, no nemo … just the ppa.
Keep in mind … any bugs on the current bionic-desktop ISO from the repos will migrate to the ubuntu-unity-ppa-amd64.iso build.
Regards…