I worked on this project at Google this summer as part of my internship (I wrote the dead code elimination phase). I think this is more useful for sharing business logic code between Android, iOS, and web (via GWT) apps without re-writes in Objective-C and JavaScript. Keep the respective presentation logic in ObjC+Interface Builder, JS+CSS, etc. I'm not sold on the idea of developing iOS apps alone in Java since the Apple tools are so good.