I think Osiris is secretly working/ being controlled by/for the nine, I recall him meeting with the nine on Europa, I also like to believe that the nine are the nine remaining Ahamkara, Ahamkaraa are thought to be extinct but I highly doubt they are. Ahamkaras are creatures that just by a single touch can change someone or control them The key point that really convinced me, Bungie loves to make connections to real life history and stories, they undoubtedly know the story of Beowulf (and by extension Grendel and the Hobbit), not the shitty shader, the old English tale. In these stories there is a great dragon who holds untold wisdom, knowledge and power, however, they only thing they ever want and can never get enough of is gold. Or more specifically, gold coins. They hoard and sit on these vast piles of gold and are content. Now who is collecting coins like a madman while dishing out crazy powerful items? Xur. He brings out the items the Ahamkara/Nine wish to bargain off and in return he brings in loads of strange coins that his masters can keep for themselves and sit upon. If Osiris did indeed visit the nine he could be being controlled or working for them at this tie. Clearly though this is all THEORY though.