ClojureScript could ship with a new REPL environment (compatible with cljs.main's --repl-env feature).
With this new REPL environment, Graal.js's polyglot capability can be enabled by default, thus allowing direct interaction with Truffle languages.
Here is an example, based on a spike into such a feature:
Over the long term, the graaljs REPL environment could be considered a modern replacement for the use cases currently satisfied by the nashorn REPL environment.
Nashorn will evidently be deprecated with Java 11: http://hg.openjdk.java.net/jdk/jdk11/rev/fb7800b66c92