This is my theory, they vaguely align with aethers makes me think first bond smith spren were analogous to Aethers. Re-shephir and midnight essence, the wind as the zephyr aether, night watcher and verdant aether. Some were unmade by odium into the unmade. I don’t rember why/where but I recall there being evidence that the sibling and storm father predate the night watcher, who I believe was an attempted recreation of one of the ancient bond smith spren by cultivation , probably based of the verdant aether