The whole case isn't actually returning. Bloom and Knightley are both off the film, they said they didn't want to do another. There's trouble at Disney at the moment too between all the execs. A guy called Cook was the one who persuaded Depp to come back for number 4 and it looks like he's about to get the chop, so it's all a bit touch and go at the moment.
But if it does get made, it'll be Sparrow-centric. Why else do you go watch a PotC movie anyways? ^^