Able to use the kraken???

[Dr. Zeppers]

The Kraken played such a temporary role in the films, probably the shortest role in the film. Spotted in the middle of the 2nd movie, swallows Sparrow at the end of the 2nd, and its only appearance in the 3rd movie was it dead, rotting on the beach! The Kraken was Davy Jones "pet", and did his bidding and noone elses. It was also killed off in story by Davy Jones himself (as stated by Lord Beckett in POTC#3).

They would also need to give us a means of defending our ships against it because it would be available im SvS too.

It would be neat, but I dont believe that its feasible from the story line perspective, the playability perspective, or the performance related issues pointed to by Sven.