It is clear that a lot of very important and practical work had been delivered with Java/JVM. But the original point was not about what is possible, but what is

It is clear that a lot of very important and practical work had been delivered with Java/JVM. But the original point was not about what is possible, but what is optimal. Kotlin, from the little I've seen, appears to be largely a syntactic variation of Java, so there is certainly good impedance to JVM. Clojure is less so, and here lies the reason everyone curses about its backtraces.