At the moment, the subtask management is too tedious, say, I create 3 task, later I decide to make them subtasks，I don't have a direct way to do so but to copy each title and then copy each under the new task, which is frustrating. Another drawback is the UI design, many aspects such as subtasks and description are hidden too deep rahter than flat in the UI. You have to double click a long way to see something otherwise could be shown with one click or mouse over, which is also inconvenient.
It will accelerate the workflow by enhancing the drag and drop function and UI

--------------------------------------------Drag and Drop----------------------------------------------
Drag a task without subtasks on another task(with or without subtasks) to convert to a new subtask under the target task.(you need to figure out a way to deal with the details like description and etc)

It will also makes sense to drag a task with subtasks on another task(with or without subtasks) to create a project.(pop up a project creation menu maybe)
-----------------------------------------------------UI---------------------------------------------------
1. Put the icon before a task with subtasks, click the icon to show the subtasks in a drop down list with indention rather then a popup menu can enhance many aspects.
1.1 Easy to click without move a long distance.
1.2. Show the synopsis in one page to see the big picture
1.3. You can add drag and drop and tab/shift-tab function to convert a subtask to a task or vice verse.
2. Click or mouse over the description icon to show it in a popup menu.
3. Add back and forward in the toolbar to ease traverse around.

-----------------------------------------------------Miscellaneous-------------------------------------------

Show the hyperlink in the task title or subtask as a clickable link rather than a text link.
Always have a convert back function for the "covert to project" function.