I upgraded to the Sierra beta yesterday and the i and h keys were reversed on my external mechanical keyboards. Seemed a bit strange.

Upgraded to the Sierra beta?

Why? The real thing has been out since September 20.

10.12.1 beta is already out

Happened to me too: https://forums.developer.apple.com/thread/64304

I downgraded to el cap solely because karabiner stopped working in sierra.

My 'a' key didn't work either. I filed a radar yesterday.

System Preferences > Keyboard > Keyboard > Modifier Keys... > Set Caps Lock Key to Escape

I don't believe 'Escape' is one of the options. On macOS Sierra, as for every previous version for me, the only choices to remap through the prefPane are "Caps Lock", "Control", "Option", and "Command".

Hence why Seil/KarabinerElements is the first thing I install on a new Mac.

Apparently the latest beta (10.12.1) has support for this natively.

https://github.com/tekezo/Seil/issues/68#issuecomment-250195...

Interesting. It really has, but I didn't see it before.

I was using Karabiner to set caps lock to control AND escape when pressed independently, something extremely useful to use Vim and command line. This doesn't appear to be supported, unfortunately.

Oh, well then! Looking forward to the first Sierra update, in that case :)

I really did not expect Apple to finally fill this gap that has been around for so many years.

Yeah, sorry I didn't specify. I am running the latest macOS Sierra beta.

And at least for me, the system preference switches simply don't work for my external keyboard (it can't seem to fully understand the difference between an internal keyboard and an external keyboard).

OS X nor macOS have the option to set caps lock to escape. This is why people who want to do this use Seil or Karabiner Elements.

I map escape to jj which is pretty useful. Thanks to some article somewhere years ago fir that.