Sometimes I make tasks that I eventually realize are subtasks of a more general parent task, and I want to be able to easily create a parent task and then drag and drop them onto it to consolidate my task list and save space.
Right now, I can get there, but it’s not easy: I have to go into List View (the more I use Asana, the more I use Board View!), select the parent task to open its detail view, and then carefully click on the wannabe child task without actually selecting it (which would open ITS detail view instead!) so that I can drag it into the parent task’s subtask list. This is cumbersome, and it would be cool if I could just drag one task onto another in order to convert it to a subtask, which is similar to what is requested here - Drag and drop subtasks to other tasks in list view - except that request is specifically about moving subtasks from one task to another, not about converting tasks to subtasks.
My solution is more generalizable, and part of why I am proposing it as a new topic is because if it were possible to simply drag one task onto another to create nested subtasks, that functionality would hopefully also work in Board view, and the desire for that behavior is what actually prompted me to come and submit this request! 
The fact that there IS a way to make drag and drop to work in List view is enough to satisfy me most of the time, but it’s admittedly annoying to have to toggle between the views, and the extra steps I described above (having to carefully move tasks back and forth between the detail pane and the main list to change them from subtasks to tasks and back again) is tedious, so I don’t always have the patience for it, and today was a day where it was annoying enough that I felt like I should finally speak up.
Thanks for listening, and keep up the good work!
<3 Kynthia
