I have been taking a quick survey of Clojure web frameworks, particularly in terms of their use (or not of asynchronous handlers).
The leading contenders still seem to be Luminus and Caribou. Hoplon seems to be the new Pedestal for completely Clojure development.
I also came across Joodo which seems to be a new framework focussing on middleware features.
So the short summary is that all of these frameworks use Jetty and a lot of their functionality seems bound up with lein ring integration so switching Jetty for HttpKit does not seem trivial.