I don’t understand all this love for Lua. I’d like to see the v8 engine make it in via this interface. One engine to run them all. Except Lua … or C# or … sigh. List of languages that compile to JS · jashkenas/coffeescript Wiki · GitHub
Although, while I don’t know if Awesomium (or equivalent) is freely integrated into the game UI, that might do just as well, perhaps. In the game FireFall I was thinking about creating hooks in Lua for writing scripts in JS from the Awesomium UI overlay/shell, which supports Canvas rendering overlaying the screen, and nearly went for it until I found out they might pull it or some of it out.
And don’t tell me V8 is “too scripty to be performant”. Half the stuff at http://chromeexperiments.com/ could prove to do wonders as examples of what could be done as GUI or async background tasks in the Unreal engine.