How can I re-enable the (display) sleep shortcut on macOS Sierra?
Things definitely have changed:

⌥⌘⏏ (Cmd-Option-Eject) to put your machine to sleep no longer works in Sierra.

Supposedly, ⌃⏏ (Ctrl-Eject) has taken its place, but it doesn't work on my late-2012 iMac.

At least according to the documentation, that is the only change - compare below.

Sadly, you cannot bring the old shortcut back (at all?), because defining keyboard shortcuts in System Preferences &gt; Keyboard &gt; Shortcuts &gt; App Shortcuts doesn't allow you define shortcuts involving ⏏ (Eject), and, in fact, even shortcuts that are permissible do not seem to put the machine to sleep (flickers briefly, but stays awake).

Sleep-related shortcuts as of macOS Sierra:

Source: https://support.apple.com/en-us/HT201236



Sleep-related shortcuts as of OS X El Capitan:

Source (link effectively dead, redirects to the Sierra page): http://support.apple.com/kb/ht1343