It would be great to filter by parent issue in a Portfolio Plan, like the filters for Team, Project, etc that already do exist.

In JQL, we can use issuekey in childIssuesOf("IN-116") since JPOSERVER-1897, but in the plan and in the program it would also be helpful to reduce the scope-view to all the children of out parent-links (IN-116) to focus on all the todos in for that Initiative.