User blog comment:OverlordRocks/The Ethereal Divide in S7?/@comment-27507964-20160502023358

Cole could have a connection to the Ethereal Realm because of how he became a ghost. However, he still has enough connections to Ninjago to keep him from becoming part of Yang's chained students. It could be Yang has come back to claim Cole as one of his own.

Maybe the Ethereal Realm connects more than just the realms, maybe it connects all moments in time. The events of Skybound and Wrong Place, Wrong Time could be lost somewhere in the Ethereal Realm.

If Yang has some control over the Ethereal Realm, which he seems to, he could bring the villains forward to help destroy the ninja and claim Cole as his own. This is actually kinda dark.