I enjoyed their storyline too, but honestly, what more can you do with their characters?

Will's off sailing the seas for ten years with no way to be in contact during that time, Elizabeth's knocked up with his kid, and if the scene at the end of the movie is any hint, the next time they would even be able to become part of another storyline again (outside of perhaps some cameo appearances from Knightly.) is ten years after the end of the third movie. With Bloom and Knightly unwilling to do another movie anyway, what more can be done?