So did I! Very interesting use cases and approaches, a must-watch for all who use subtasks extensively.
I too advise clients to use them lightly, more like a personal checklist for the assignee of the parent task, avoiding to assignee others to subtasks due to the reasons mentioned like not showing up in Workload (although subtasks in timeline seem to be almost solved!
One thing that you may have included (perhaps not available at the time of recording) is that you can click & drag a subtask from the task details pane into the project list view, which literally promotes a subtask into a task whilst also ‘moving’ it into the project. And you can actually do the reverse too!
is what happens to Asana when you do this, but it surprisingly works!