Jonathan,
Good to see one of the things you are doing these days! This looks cool!
Also, you might check out the RetroLab project, which aims to create an interface very similar to the classic Notebook, but with pieces from JupyterLab, using the JupyterLab extension system:
https://github.com/jupyterlab/retrolab
Finally, we are making progress in JupyterLab on a single-document-focused mode ("Simple mode", toggled with a switch in the bottom left of the jlab 3 interface) to help address the concerns that the lab interface is too much in some workflows.
Thanks,
Jason