I'll add that there's an emacs Jupyter mode if that's of any interest.
I agree in principle that a better plaintext format could be interesting, but I don't see how embedding graphs etc could be easily done without a special interface of some kind.
That said I can imagine a mode where you simply have any editor open on one half of the screen and a browser that autorefreshes on the other.. this is more or less how I work with Emacs and Evince when working on Latex and it's great. Synchronising vertical position with the cursor position might be a challenge.
