I’m not saying that this will never make it into Joplin. First Laurent has to accept it and then you will have to find someone to implement it.
Couldn’t agree more!! It also becomes easy to navigate in large notes
I am working with large notes and I also think that folding sections will be extremely useful to help navigation within the relevant parts of a note in both editor and rendered HTML (could be an option for both).
Even if they are unfolded on each note reload, it is better than nothing (a simple "collapse all" button would be nice though).