"You can then use Interface Builder to create an Aqua GUI for your script. To make Java a first-class citizen on the Mac, it would be nice to have this Interface Builder functionality for Java projects as well."
We.. do have it. Project Builder and Interface Builder let you create Cocoa-Java or Swing or AWT applications. And, indeed, Pure Java tools, so why use Applescript at all? Project Builder can be your IDE, to compile click "Compile", and to run click "Run". It's nice to know that you can use AS to make a seperate application to do that, but not all that helpful, unless I've totally missed the point.