Use case or problem
When I apply “Toggle numbered list” (from Settings/Hotkeys) for easier readability of editor text it is more useful to get numerated lines, rather then all (1.). Additionally it is useful for further re-numerating / fixing numeration when adding more lines in between, etc, with Untoggle+Toggle again action.
Proposed solution
It seems extremely easy to count lines in the script and implement, so i think any additional comments would just spend time that we are all trying to save while using amazing Obsidian 
Btw auto-numeration is already implemented on Enter/new line, since it counts from the last line, it creates hassle to fix that. Feature above will give a great tool to fix that.