It would be nice if you could provide a way for us to hide some advanced editor options behind a button (group them) or allow for a button to expand the list of editor tools for a user. 
My use case is that we have users who want a wide variety of advanced buttons to be present, like subscript and superscript, but I don't want to clutter the view too much for regular users.

+1

There might be available CKEditor plugins. Check their site as this request is out of Invision's scope.

https://ckeditor.com/cke4/addons/plugins/all