Is it possible to detach a notebook widget into an external browser window? This would allow one to display a widget on another screen, for example. Like %matplotlib inline ==> %matplotlib qt, but using the browser and HTML/JS instead of Qt.

If not possible, here is a possible alternative: "fake" popup widgets in Javascript that live in the same browser instance (e.g. jquery UI dialogs). For multiple screens, one would need to resize the browser window to span the different screens.