I was thinking about building a similar deck with the cards from the new set!
Why the Orzhov Guildgates? Put in Sunpetal Groves/Woodland Cemeteries/Isolated Chapels instead. Seeing as you have arbor elves in there, you are still considering the blocks that will be rotated out in September, so these lands are more worth it than guildgates.
I really like the idea of extort with the
archangel of thune, since each trigger activates separately, your creatures will get huge quick. Perhaps a 3rd
Archangel of Thune will ensure you have that combo more often will be better, and since you have ramp having one more creature with CMC of 5 wont hurt. I would personally take out the
Obzedat, Ghost Council for the 3rd archangel.