Along the same lines, I would love to see a syntax something like this:

mynotebook.py

    ### (cell boundary)
    """Top-level unused strings (docstring-esque) rendered as markdown"""
    def add(x, y):
      return x + y
    # jupyter-output-hash: 0123abc (which would link to some external key-value storage for the project)

Anything in something other than the primary language could be in something like `execute_scala(""" scala code """)` - which would execute properly given proper globals.

As long as the output-hash storage is treated as append-only and is highly available (output cells could even be encrypted for security if this was a public cloud service, or you could even use a local or shared filesystem), then this file would not only parse and run as a perfectly valid Python file, but it would also hold references to outputs in a source-control friendly way. IDEs could show the cell outputs inline. If you rerun your notebook and get different outputs for some reason, `git diff` tells you exactly where things changed without being too messy. Basically, put outputs in off-chain storage, and just be a literate code file.

I feel like this would address most people's needs, no?