How do you achieve this with just System Preferences? On 10.11.6, I see the System Preferences -> Keyboard -> Modifier Keys allows re-mapping to Nothing, Control, Option, and Command, but not Escape. Is this a macOS Sierra thing? Tell me your secrets!
Check out Karabiner and Seil- you can even use these to map "tap capslock" to esc and "hold down capslock" to ctrl. (Seil has some issues in 10.12, but they're working on it.)
They have made karabiner-elements to do just some basic things and which works with sierra. I had a problem with it though as it remaps F-keys by default and it was clashing with Palua on 10.12
