I want to thank you for the idea for the deck. This is a very good looking build. I have been looking into an Orzhov deck for a while, possibly working the Extort mechanic into my Black/Blue hand control deck to give me that extra survivability. However, can I suggest one card for you to work in?
Exquisite Blood. "Whenever your opponents lose life, you gain that much life." It is great in any black deck, but I think in this deck it would truly push the
Blood Baron into its full power, and quickly, despite its 5 drop cost. It is merely a suggestion, but I hope it helps!