And those questions have not abated. Many people continued to investigate. And the situation is now somewhat improved.
We can now make to bootable iso with the following commands:
hdiutil create -o /tmp/HighSierra.cdr -size 5130m -layout SPUD -fs HFS+J
hdiutil attach /tmp/HighSierra.cdr.dmg -noverify -mountpoint /Volumes/install_build
sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/install_build
mv /tmp/HighSierra.cdr.dmg ~/Desktop/InstallSystem.dmg
hdiutil detach /Volumes/Install\ macOS\ High\ Sierra
hdiutil convert ~/Desktop/InstallSystem.dmg -format UDTO -o ~/Desktop/HighSierra.iso
and then you can rename HighSierra.iso.cdr to HighSierra.iso.
You can then use this to burn it to a dual layer dvd:
sudo hdiutil burn /Users/YOURNAME/Desktop/HighSierra.iso
where you replace "YOURNAME" with the username for the account you are logged into at the time.
and then boot to startup manager with option key to select the dvd and install High Sierra from it.
BUT - as it is formatted as hfs+ it will only boot up computers in hfs+. It won't boot computers already formatted as apfs.
Attempts are still underway to make an apfs version of the bootable iso which may lead to a dual bootable bluray capable of booting up computers in both formats.
PS. As of only a few hours ago I can confirm that this bootable dvd not only boots but also successfully installs High Sierra.
