The primary challenge is RAM. The (simplistic) approach I took with establishing a ClojureScript REPL is to have the standard library available, and that requires a lot more RAM than most Espruino boards have. Even with the ESP32, I had to make a few tweaks to Espruino in order to make more of the ESP32's RAM available.

Perhaps a more sophisticated approach could be devised involving "faulting in" ClojureScript standard library functions on demand as they are used, and by doing this use less RAM and reduce startup latency. If that were done, things would run on a broader range of chips (less RAM needed).