Some people might consider it simpler (I would be one of them), and having the choice to leave out the // would benefit those people, no? Of course it's another idea to add on the pile, but isn't that the case with any good idea? And using id:// isn't confined to the CB - personally I generally use id:// tags instead of just surrounding text in []s, because I don't like the idea of my post pointing somewhere else in the future when someone posts another node with the same node as I've linked to.