The ability for the browser to modify files directly on my workstation outside of caching folders sounds like a recipe for disaster.
2) to enable this feature, you first need to go to a "start connection" screen (not showed in the video)
3) you need to click on a dialog to accept any incoming connection
Personally, I would love it. It would make my life easier to have a full IDE within a browser. However, I would never be comfortable with the security tradeoff and would never enable it.