I didnt find anything about thison issues/suggestions and i think this would be amazing.
Instead of using JS/Nashorn as a Script-Language, just let us use Java/Kotlin.
-It would have better Performance than JS (and SenkJu also said in a onEvent for TextRendering that he doesnt want to include it bcs Nashorn sucks at Performance)
-it (probably) isnt that hard to make
-in the ScriptAPI you usually already use the Java Classes, but with a js-wrapper around it
(i suck at js, and probably some other people do too)
But i also could see why you wouldnt want to use it (for example people who obfuscate).
Still would be very nice to be able to make 'Scripts' in Java/Kotlin, because these are languages you can actually use.