It would be nice to move task from a bucket to another bucket within the Update a task action or Update task details action.
I would like to do something similar - track the status of the task in planner and use it to update the status of a sharepoint list item assocated with the task.
The ability to move tasks between buckets is fundamental to Planner. The ability to automate tasks is fundamental to Flow.
What is missing is the ability to automate the movement of tasks in planner using flow. This massive oversight means that these two powerfull tools cannot be used together. There is no point being able to Create, Get, List and update tasks if one cannot also move the tasks based on set criteria.