I think the idea for :repl/quit was because of figwheel and other REPLS that piggieback on nrepl
Mostly because if you quit the REPL it would stop the compiler, so instead it quit the ClojureScript repl but returned to the Clojure one... But I may be wrong too :)
Interesting... For Joker I decided to just add joker.core/exit
function. I think this is the most straightforward approach.