One downside of Neptune is that Pluto’s save files do not store the outputs of the cells. This can become a problem if the outputs depend on the order you execute the cells in. After saving and reopening a notebook, you might be unable to reproduce the outputs you had before.
So, I think you should think of a way to store outputs in the save file somehow. If you figure out a good way (without losing the “notebooks as code” idea), I think that it might be nicer to add ways to conveniently use such a format to Jupyter (rather than making a new tool).