Allow for accordion menus

Our Outline users say that they would like to see accordion menus on some pages. They like the way accordion menus work on long list pages because accordion menus break up lists. As a web developer, I like them because in theory, it should (on average) put less stress on the server, since the client handles all expansion/revealing. Users have told me that they don't really care about how the accordion menu looks aesthetically, as it serves more of a functional purpose:

Here is what I mean by "accordion menu":