This would make life a lot easier! +1 for this feature. I don't know what framework they're using for their UI or if they are using one, but Material UI has the accordion component: https://material-ui.com/components/accordion/. I'm sure there's ready made stuff out there that could be brought in or adapted to the markdown structure.
It would be really useful to be able to lay out multiple cursors so you can edit many lines at once, similar to what you can do in Atom or in other dedicated text editors. I've traditionally seen this as holding command and clicking to place the cursor in multiple locations.