Thanks for opening this.
One thing to keep in mind, some of these modules may be OK just keeping on the singleuser jupyterlab environment, and not adding to the full image which is also used on the workers (things like ffmpeg and xmovie).
To what extent would this be solved by installing these modules in a persistent location in your user directory? Something like
pip install --user cmocean
Will install into /home/jovyan/.local/.... It will persist across sessions and is already on sys.path so the usual import cmocean will work.