Recompilation of running JS without having to restart it. It's like Bret Victors talk, when he demo's rewriting code (http://vimeo.com/36579366 , for example at 5:45). I'd like to show a working proof of concept of this as well as demo other parts of his talk that are up'n'running, and how you'd go about coding something like that.
So a crazy nerdcore JS rewriting and tooling talk. Guaranteed to blow peoples minds.