The writers said that when they begin to work on Pirates 4, it will be a seperate story from what we've seen already. I don't think then that it would be a prequel.
I don't know then, either, if they would work it in between the ten years or not. I would like to see W/E in the film for at least some of it, but maybe they're son will do some adventuring of his own while Will and Liz enjoy being retired pirates or some such. 😄