Having seen several trailers of the 4th Pirates movie, "On stranger tides", and also reading about the storyline etc I think it was better to leave Keira out. It really would have been hard to fit her in, at least the Elizabeth character. Lets be honest, that whole Will/Elizabeth/Sparrow storyline went to its conclusion and there wasn't anything you could do with it anymore. Sure they could have leave Will out now and just have Sparrow and Elizabeth as a couple now but to me that would be unrealistic. Besides, I think its better for Keira's career to move on from the Pirates franchise.
Im not much a fan of Cruz either but I think she fits in well for the new Pirates movie. Im actually looking forward to watching it, come end of May.