Be aware: Sierra breaks Karabiner and Seil. You'll need to use Karabiner-Elements, which has far less functionality than Karabiner. Notably, you can't remap caps lock and you can't assign to more than 2 keys, so caps-lock "hyper" is out.
Seems this is the place to look: https://github.com/tekezo/Karabiner-Elements/blob/master/src...