I was also interested in this feature. The OP touched on a better idea than the current version, which only offers a partial solution.
Problems:
1. When dates are "independent", a subtask's due date can be set after the due date. That doesn't make sense.
2. The % done is either a sum of the subtasks or arbitrary. That makes the parent issue a container, rather than an issue.
Fix:
In addition to "independent", there should be:
1. A setting that keeps child end-dates within the parent scope. That may or may not also limit start dates.
2. A setting that calculates the % done as subtasks + parent task.
As a simple example:
Issue: Drive my car to my house
Subtask: Fill car with petrol
Subtask: Replace punctured tyre
With Fix 2, the % Done can be a sum of three issues.
If the parent issue is not allowed to be part of the equation, then I don't see how we can structure dependencies.
- Issue: Drive my car to my house
- Subtask: Prepare car to drive
- Subtask: Fill car with petrol
- Subtask: Replace punctured tyre
In this second example, "Prepare" is dependent on two subtasks, which is good. However, once "Prepare" is complete, so is "Drive".
I can add another subtask to represent the actual driving:
- Issue: Drive my car to my house
- Subtask: Drive my car
- Subtask: Prepare car to drive
- Subtask: Fill car with petrol
- Subtask: Replace punctured tyre
But that means breaks the dependency. I can set "Drive" to complete, even before "Prepare".