We have heard about Ul'dah's sister state since 1.0 (I think it was in the 1.0 miner quests) I for one would love a Sil'dih ruins dungeon. Sil'dih is about the last 1.0 tease we still don't have access to, an ancient civilisation and a major part of the lore of Eorzea. It could also fit into a story arc looking into the history of Sil'dih.

Based on the lore we have seen of it Sil'dih could be a very fun dugeon.