You brought us FF13 heroine so there is no reason not to bring this iconic villain to FF14 as the hardest Extreme Trail in 2.2.
I'm a big fan of Sephiroth, I think he is the second best Villain in FF history and for sure top 5 in RPG games history. I have faith in the story writers to find a way to bring him to FF XIV. He should be hard, unforgiven, powerful and even when we win against him it should not look like defeat but just him exiting the scene for whatever reason. Honestly, I would not even mind if he was Turn 10 Coil last boss in 2.2.
I WANT Sephiroth! nowz!
P.S. don't forget to add epic CGI just for him kicking everyone behind like a boss ^^.
Edit: Seriously boss fight with "One Winged Angel" playing in the background...ZOMG.