This would need to be implemented first, yes? https://wunderlist.uservoice.com/forums/136230-wunderlist-feature-requests/suggestions/12899580-sub-task-due-dates
First, Wunderlist would have to actually capture when your tasks were completed before you could sort on them, yes?
This feature is nearly a MUST HAVE. An Alternative approach would be to link tasks to other tasks and therefor make them subtasks by relation. This would remove the need for the subtask concept altogether. All that would be needed would be a means to prevent a circular relationship where a task which is a subtask by relation could then become that task's parent.
This would be particularly useful if there was some way to assign due dates to subtasks, which you presently cannot.
I want to migrate from iCloud reminders to Wunderlist and the thought of having to manually move all of these tasks just seems stupid. I can't believe that no one has created a tool to do this- seems like an obvious way for Wunderlist to get people to move from Apple Reminders to using their product