Java source code does not want to be a target language. It has restrictions against logically sound constructs that would be bad Java practice to write by hand. Lex Spoon proposed a plan for an intermediate step, "Loose Java," which we have christened Jribble (pronounced "Dribble").
Jribble is essentially Java with the interfering restrictions removed. Lex: "It's like a puddle of Java. It's also like drivel, which is appropriate enough for a language no one writes and no one reads. Computers can entertain themselves with it well enough."
While far from a spec at this point, the general concepts of Jribble are:
Our efforts so far have been to create a new "jribble" backend to Scala that produces output along these lines, and parallel patches to GWT to understand Jribble input. As we expose more of the issues through this process, we'll formalize Jribble -- as a spec. This hopefully will open some doors to translating other languages into a form that GWT can compile and optimize.