Any way to get the displays menu in the menubar? Running OS X El Capitan (late 2013 iMac). Unfortunately it looks like the "show displays in menu bar" option was removed from System Preferences. Is it possible to get the menu back?

PS - opening the Displays.menu file (/System/Library/CoreServices/Menu Extras/Volume.menu) adds the menu back, but as soon as I click on it, it disappears.

Also, if it's of any relevance, I've got HiDPI mode enabled (but not active). 99% sure it doesn't matter, disabling HiDPI mode didn't affect the issue.
You could use a third-party utility named Display Menu. It's available in the App Store for free. I've been using it for quite a while and it has work just fine.

By the way, when I open /System/Library/CoreServices/Menu Extras/Displays.menu it puts the same menu as the [] Show mirroring options in the menu bar when available check box in System Preferences > Displays > Display, does when checked, but does check the box.