Things are getting better. I was aware of them, but jupyter is the 600 pound gorilla in this area.
I wouldn't use observable, as you are tied to their web service, and I've had too many companies close to use such a service for important data. Pluto is promising, but (I believe?) Only supports Julia, which is growing but still not that popular, or known.
True, but you have access to whatever Python libraries are installed, and your output is web-based. So you can potentially output anything a browser can display, including interactive 3D graphics and widgets. You also have access to the command line in Jupyter, so you can run whatever shell commands you like.
Because the data is inside a data structure like a table or dictionary that you can output, iterate and map over however you like with the various Python and library methods or functions.