Well, it wouldn't make sense to add the Bayou portion, since WDW's Pirates is placed in a section of Adventureland themed to be the Caribbean.
But, as to the rest of the attraction, it would be impossible to simply add another couple hundred of feet to the attraction without virtually starting over. I don't think Disney would invest that kind of money in an attraction that's not going to attract enough additional people to the parks to pay for it.
So, the short answer is "no" I don't believe this will happen. However, if POC II & III are successful films, I do (unfortunately) think the attraction will be made to be more like the films.