Regarding protocols, I believe this is the main thing. Since clojure can be implemented in terms of protocols instead of interfaces, it would be one less thing to tie to the host language.
It’s not quite directly addressed, but Rich does talk about it in the clojurescript language release announcement. Clojurescript IS implemented in terms of protocols. I believe his initial mention of protocols is at the linked time, ~11 mins in but I think he might come back to it later (I listened to this a few weeks ago).
The whole thing is probably worth a (re)listen if you’re interested Rich’s thoughts on a fresh implementation of clojure a few years after clojure. (Of course with the major differences and tradeoffs involved in cljs).