Hi @Chan 
In case you have missed it, we have recently implemented as a part of the New List View, the subtask indicator in Asana 
Now, you are able to see the number of subtasks within a task—without having to click on it —from List, Board, Calendar, Workload, or Timeline View. You can find out more about it in here: Have you checked our last last blog article? If not, hurry up, it includes a cool little surprise! 🎁
While I don’t have any information to share regarding this functionality on mobile, I’ll make sure to keep you posted as soon as I have an update!
Have a great Friday Chan!