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.
-WarrenLarry Jaffe supported this idea ·
This item is still in the works.
Also, thank you for the additional feedback. I will circle back to the feature team and provide a new update soon.