I think they can come up with more sets if they decide too. I don't think they've necessarily run out of ideas as much as I think they’ve run out of easier ideas.
I can imagine a majority of sets they might produce (Blacksmith's shop, Barbossa crew battle pack, Kraken, Shipwreck cove, British fort in Port Royal) if they intend to continue this line.
All I can do is keep my fingers crossed and hope! I personally thought the PoTC sets were pretty good, and I hope it gets continued.