Excited about IPython notebooks generally or possibility of editing them on GitHub?

If you want one to edit, try here: https://cloud.sagemath.com

There are a lot of tools for editing notebooks, and they're complex. I also don't use their online code editor, because mine is better. Through my personal experiences, my assumption is they'll never take on that project.

you cannot work on it yet.

It sounds like you expect this to change. If you could actually run the commands, where would the computing power come from?

If you go to https://try.jupyter.org/ , you'll get a temporary notebook server in a Docker container, courtesy of Rackspace. It's automatically destroyed after a few minutes of inactivity.

editing does not either imply running code. Markdown cells could be easily edited without a running kernel.