Karabiner doesn't work at all with Sierra. There's some "new" project called Karabiner Elements is supposedly half-finished, but yet people keep donating hoping they'll get something usable soon. Not holding my breath and it would be completely new and will likely lack useful features of the abandoned one.
It would be more useful to more people to temporarily fix Karabiner and work on Elements later, but no, gotta ignore paying users and stick to "the plan."
Elements is a bridge while the main project is rewritten. (It's in the name..."elements" of the original project.)
They stated in several places that it can't be "temporarily" fixed due to major structural changes to (I believe) the keyboard driver in Sierra.
Also pretty sure that Karabiner has been free forever. (Donations accepted, but you know how rarely that happens.)
Just keeping the record straight, as someone who loves the app and, yes was temporarily inconvenienced, but bravo to them for rapidly putting out something to tide users over.
It would be more useful to more people to temporarily fix Karabiner and work on Elements later, but no, gotta ignore paying users and stick to "the plan."