Actually, I went ahead and just asked him. This was his response (if you’re reading this for some reason, Lennart, thanks again):

  > CarbonOS is close, and GnomeOS too. 
  > and here, we build something generic to create images from Fedora/debian/suse/arch… distro packages:
  > https://github.com/systemd/particleos
  > There‘s a lot going on in the matrix channel of mkosi, I would recommend taking a look.