I want to be able to use the 'parent link' system with Story and Task issue types. A Story is used as a user story (As a user, I want xxx). I have then Task issues that implement this story (I usually have different Tasks per platform (iOS, Android). I don't use sub-tasks because I want to developers to be able to split out their task into sub-tasks if need be. If I would use sub-tasks, this is not possible anymore.
I would like to view this hierarchy in portfolio as well of course.