Cool idea. One of the things that make web IDEs impossible to use for me is that I keep hitting Ctrl+W trying to close the tab in the IDE, but instead closing the browser tab with the IDE. And you can't rebind Ctrl+W with JS, because that's something spam sites would abuse. Maybe you could build a web IDE that uses the browsers tab system with this. This would also mean support for multiple screens, which even desktop IDEs don't support.

EDIT: I don't really get the demo app. How do you open a new window with it?