Serve text-based notebooks on JupyterLite once supported

[danielballan]

The Jupytext plugin is serving Markdown which the front-end is then trying to parse as JSON. Keep an eye on jupyterlite/jupyterlite#731.

[guenp]

Hey @danielballan ! I've been wanting to see if we can make the executable notebooks work with thebe-lite (similar to this example but using JupyterLite instead of MyBinder), is that similar to this issue or should I create a new one?

[rossbar]

@guenp no opinion on whether this needs a new issue or not, but I very much like the idea!

[guenp]

OK I think it's a different issue: #70