It would be great to have collapsible markdown headings just like the notebook extension "collapsible headings" in jupyter. Notebooks tend to become very large very quickly and this feature would greatly help us.
This is now a feature – please check it out! Cells that appear after cells containing Markdown headings can now be collapsed into the heading cell.
Patrick Costello commented
It's great you've added this feature.
Would also be good to add a 'collapse all' button at the top somewhere so you can quickly compact your notebook and open up the cells you want