I also thought about this, but I have postponed it for now, because there are some implications with this (see here: https://github.com/jotaen/xit/discussions/2). So I thought it’s better to properly think this through beforehand.
I use subitems pretty heavily in my todo_notes.md file as well; to work around the concern over conflict of state, I pay attention to only the checked status of the `large task`. If that parent is not checked off, I know there are still pending subtasks. So I won't really care if there are un-checked subtasks; as long as the parent task is checked I know I can ignore it and move on. Maybe that could be formalized a bit more strongly but since it's only my eyes which will see my todo 99% of the time, I'm fine with it and I know the convention.
Why no subitem?
I use this all the time.