Hosting the notebook and hosting the development environment are two different things.

It's like saying git (observable) can't be self hosted because github (observablehq) is not open source.

Just to jump in and say my comment that you said wasn't true was "... improvement over an existing literate programming environment.".

I don't argue that you might find a different notebook environment more suitable. That's totally up to taste, preferences, and silly do argue about.

But observable (the reactive notebook technology) can do everything a jupyter notebook can do, you just need to write a bit of communication code to hook up a websocket. (For me sandboxing the ui is a feature not a bug.)

And you can also self host it on a machine of your choice, and edit it locally.

We do that internally for all our dashboards.