I can understand why one might want to enable the use of the Nashorn JS engine, however I think it should have been discussed first.
The Nashorn engine is twice as slow as Rhino initially, so benefits will only appear over the long run. So there are potential drawbacks to making Nashorn the default. Also it looks like the Google V8 engine is much better than Nashorn (though maybe we cannot use it). Furthermore, I don't understand why the change should only affect the If Controller. Rhino is also used by the _javascript function. [The BSF and JSR223 elements also support Javascript, but that is a separate issue entirely]
