I find that the majority of dependencies I set are amongst subtasks within the same task or amongst tasks within the same list. When I bring up dependencies, I would find it helpful if, once I clicked on waiting on or blocker, the current list or task was drilled into.
It might also be nice if I could Cmd/Alt-drag one task or subtask onto another to quickly set a dependency. Maybe Cmd to have the dragged task block the other and Alt to have the dragged task be blocked by the other.