I wassnt just looking at changing the GDM screen but also the plymouth theme to match.
At the time I was only thinking about Ubuntu and I thought snap would be the easiest way of distributing the software. I was / am waiting for Snapcraft to implement a alternate hook:
Then I remembered you need root to update the grub color and it kind of fell apart.
I suggested a small GUI with some tweak options but got no response so it kind of died out.
To be honest if that concept becomes reality it would be better.