macOS Sierra: How do you enable shutdown keyboard shortcut (Ctrl + Opt + Cmd + Power)?
Ctrl + Cmd + Opt + Power/Eject still works in macOS Sierra. I just tested it with an upgraded install (El Capitan to Sierra) on an MBP Mid-2014. Please see if another keyboard shortcuts overrides the shutdown command:

System Preferences > Keyboard > Shortcuts

After upgrading to macOS Sierra my keyboard shortcut for Spotlight (CMD + Space) was changed to Ctrl + Space. I had to change it manually to restore the functionality.

Edit:
John, please do the following: Backup all PLIST-files starting with com.apple. + pbs.plist + ".GlobalPreferences.plist (in Terminal:

cp -f ~/Library/Preferences/.GlobalPreferences.plist ~/Desktop
# this will copy the file as a backup to the Desktop

rm -f ~/Library/Preferences/.GlobalPreferences.plist
# this will delete the original file


Also backup the folder ~/Library/Caches/. Now delete everything inside this folder. Empty the trash and reboot.