I work with groovy in my day job, and I have to say that it is the NBL on the JVM. It has:

* ease of adoption from existing Java developers because it's a superset of the java langauge

* the enterprise capability (which the author mistakenly dismissed it for) thanks to groovy++

* finally, if you were to change Java the way the author suggested for Java 8 and 9, then it would end up looking like Groovy anyway. So DRY and just adopt Groovy as the NBL and leave Java to be backwards compatible.