We are using Maniphest to discuss certain tasks and problems at different levels.
Sometimes the high-level discussion in one task starts to tackle details, which really should be discussed in one or more separate tasks, especially if the original task's function was to get an overview over a certain topic, and the details concern a different set of people.
What we do now is basically:
- stop the discussion
- create one or more new tasks
- insert a reference to the comment that prompted the task, and re-word the problem in the new task's description
- hit the quote button in the old task's relevant comment and copy over the quote text in a comment in the new task
The new tasks aren't really subtasks, since the original issue is usually sufficiently talked about, and the new tasks or issues are not blocking the original task.
I could imagine a field akin to "blocking tasks", but something like "emerging tasks". An there could be a mechanism to create such a task from a specific comment, for example.
The other alternative would be re-purposing the task, but then the context of the original high-level discussion is lost.