This is the most promising one I'm aware of. I tried it in the course of trying not to accept the conclusion I outlined above.

https://github.com/mwouts/jupytext

There are a few efforts on this front. Here are two that I know of for JupyterLab:

https://github.com/jupyterlab/jupyterlab-git

https://github.com/elyra-ai/elyra#notebook-versioning-based-...