Adding my vote to this also. I think we represent a fairly common user experience where we have Tasks and Subtasks that ladder to a specific request. We would like to view the Subtasks on the calendar and NOT the parent task or other associated tasks.
A good example is for email production – we only want the subtask for Send Complete to show on the calendar. We cannot filter the Calendar view to Subtasks and adding a custom field to the Subtask doesn’t work either since Asana doesn’t look for Subtasks in the Calendar view.
Filtering by a Custom Field like “Planned Send Date” also doesn’t work because it shows the full working time for the email development Parent Task which can be multiple days/weeks. (Also only allows to view specific time frames or “after today” which isn’t helpful for a full month view.