It’s very good. IMHO, it might be even a good idea to promote this on the main Coq site, to lower the participation bar. I know a lot of people tried CoCalc, but there is a free and open source alternative from the Jupyter creators - JupyterLab. See their documentation to learn more about its features. You can read their blogpost why it was created and that it is ready for the end users now. The only missing piece now is real time collaboration, which is currently being worked on.