Currently, when changing status, if you want to create a subtask the tool is making you select an existing task. However, I think the most common scenario is you'd want to create the subtask on the card you've just moved.

A use case would be "When moving a task (representing a person) to Hired status, create a subtask on that task to assign him/her permissions"

So on the combo named "Parent task", a new option should be added to select the task that triggered the event.