The sys.fn_builtin_permissions function does completely reflect permission inheritance for the new SQL Server 2014 permissions. "Parent" refers to the parent_class_desc/parent_covering_permission_name columns, rather than covering_permission column.
Permission “USER/IMPERSONATE” should have a parent of “SERVER/IMPERSONATE ANY LOGIN”. It currently has no parent. Because having IMPERSONATE ANY LOGIN grants/denies impersonate permissions on all users. There is no IMPERSONATE ANY USER currently, which would be parent of IMPERSONATE USER.
Permission “SELECT” on “DATABASE” class should have a parent of “SERVER/ SELECT ALL USER SECURABLES”. It’s currently “SERVER/CONTROL SERVER”.