I am a temp work helping to set up Blizzcon and I stumbled upon a poster that read:
Pirates Under Stranglethorn Sails! Yar!
Not sure if expansion name or just theme, but it had those words in red lettering, surrounded by lots of trees and vines. Two pirates were on either side of a gold chest, and a troll was peaking out from the left. I only had a brief glimpse of it tho