I think this is super cool. I've been looking for an editor that lets you do everything you need to in the browser.

Ideally this would let you write code and switch quickly between your site and the editor, like an IDE's run button, but all within the same browser tab - I did a quick (and very crude) jsfiddle to show this: http://jsfiddle.net/RyT3w/1/.

Like you say there are security issues but that isn't a big deal with local web dev or within a company that has firewalls to the outside world.