The main problem I see is relying on a server. Running sandboxes server-side takes up resources even when idle (the user went to lunch, or left it running overnight). Google can do it with Colab, but this is expensive to provide to the general public, so often the sandbox gets killed after a timeout.
Observable does a similar thing, but in the browser, so the cells run JavaScript. I suppose a WASM implementation could provide more languages?
Or it might be better done using a VS Code plugin or something like that. (Thry already exist.) But that means casual readers won’t be able to play with it.
In this case, running sandboxes does not consume resources when idle. There is no state, and the containers exist only for the duration of the "run" operation.
There's a database to pass from one cell to the next, which seems rather stateful to me?
If no state is cached and running a cell automatically reruns all its dependencies from scratch, that's the equivalent of a clean rebuild when using a makefile. It might be too slow to use interactively if you're doing anything heavy. It's how continuous builds work, though.
Observable does a similar thing, but in the browser, so the cells run JavaScript. I suppose a WASM implementation could provide more languages?
Or it might be better done using a VS Code plugin or something like that. (Thry already exist.) But that means casual readers won’t be able to play with it.