There is a PR to add initial support for real time collaboration in JupyterLite: https://github.com/jtpio/jupyterlite/pull/109

This reuses almost all the RTC work done upstream in JupyterLab itself.

And since this is implemented as a regular JupyterLab plugin, folks will then be able to swap it for something else and implement their own if they want to, as a federated extension.