So I can now use a decent text editor (emacs) to edit Jupyer notebooks? Great! I do wish it was possible to interleave languages like with org-mode, though. I've yet to find a literate programming/notebook format I'm truly happy with.

Edit: oh.. I misread. It doesn't support using external editors. All I want is some way to edit those text boxes with another program. I can't do any serious work in a web browser. It's awful.

I have used it quite productively for a while, but at the moment have mostly moved back to the browser for my notebooks. I can recommend to collect larger functions in a separate source file (for Emacs editing bliss) which you import to the notebook. [import helpers; reload(helpers)]