In today's "Who asked for this and why are we bothering" news...
http://www.cnet.com/news/bioshock-heads-to-apples-ios-as-premium-priced-mobile-game/
http://www.cnet.com/news/bioshock-heads-to-apples-ios-as-premium-priced-mobile-game/
I can't imagine trying to play a FPS like Bioshock on my iPad with touch controls. A Vita port would probably be doable because of physical buttons but it obviously doesn't have the huge potential market of iOS users.