Good news, this feature is partially done. :)
Planner tasks can now be copied to other plans. To copy a task, click on the “…” menu on the task. From there, you can select a different plan to copy the task to.
-WarrenPontus supported this idea ·Pontus commented
This would be a great function to implement!
Due to collaboration between teams it would be less administration to create new "local" tasks in each team area and instead send it to the team & assignee that should handle it