I took the same steps as I did a week or two ago to stand up the new notebook code (see jupyter-js-plugins README Thankfully, the webpack build problems I saw went away. Everything more or less installs cleanly now.
To run the sample notebook, follow the install instructions and browse to http://localhost:8765/ A demo can be found on the notebook PR Still no kernel / comms, only client-side UI, so not much to integrate with. There's a file browser widget, a notebook which uses a markdown parser and codemirror but as of yet no toolbar or editing. Everything is a pwidget based off phosphor, and code is written in typescript.