I need this for allowing members of the same and other organizations to replicate "best practice" applications and dependent maps and layers, so they can implement them for their own use.
This would also support creating offline backups, and for creating entirely new versions of an app along with any dependent webmaps.
This is possible currently in Portal by exporting all items in a group to an "export package (.epk), as described in Export and import group content.
In AGOL, it would need to preserve the item ids upon import, or if not possible, then use the clone_items API function to automatically update dependencies. Essentially it would allow the use of an interchange file during the normal clone process, which AGOL fully supports. Esri does something similar for their own "Solutions". Without using such a file you need to sign in as admin in both orgs in order to use the clone workflow.
ArcGIS Assistant can move content between orgs but it doesn't handle the dependencies.