really nice, was just looking at trying to use Jupyter but their JS kernels gave me issues. Being able to use arbitrary packages would be nice, babel transpiling would also be cool.
I looked into Babel but the standalone package is (comparatively) massive. Could be an optional extension, possibly.
I think it has potential for use as a way to write documentation for JS libraries, so being able to use arbitrary packages is certainly something I'd like to add. :)
One option to allow arbitrary packages that plays well with a gist-hostable style of notebook is to make use of the JSPM CDN (details towards the bottom of http://jspm.io/). I've used that for little gh-pages hosted experiments in the past. It can be a powerful way to access both the GitHub and NPM ecosystems of JS libraries.
The JSPM CDN could also provide a way to load transpilers like Babel, Traceur, Closure, and Typescript.