You can add the "application" plugin to Gradle script to execute your application using 'gradle run'.
All the prerequisites to write out a JBang script from that Gradle script is there. A Main-Class to execute. All the dependencies (Maven) to formulate the classpath to launch the Main-Class.
Adding this functionality to the jbang-gradle-plugin would allow one just to maintain a Gradle-script and write out its JBang counterpart easily.