Not the parent poster, but I suspect he's thinking of stuff like Lighttable, or Liquid. Editors that were written in Clojure, or specifically for Clojure, and had cool features that were not available elsewhere at the time. (I'm boring myself, and pretty much only ever used Emacs with Cider)

Correct, there's something I enjoy about editors designed for specific languages in mind, they feel like they're more refined. Like I use the really simple UI that Racket comes with Dr. Racket because it has some unique features, and it just works.