The solution for a custom shell is in 5.0 different to 3.0. It's now the same registry entriy as it is for a desktop windows:
HKLM\Software\Microsoft\WindowsNT\CurrentVersion\Winlogon\Shell
Yes, it is indeed like this in Win8.1SE and without data for HKLM\System\Setup,CmdLine.
However, it is not really related to 5.0 or 3.0 that have:
HKLM\Software\Microsoft\WindowsNT\CurrentVersion\Winlogon,Shell,cmd.exe /k start cmd.exe
HKLM\System\Setup,CmdLine,winpeshl.exe