A TERRIBLE idea in my opinion.
First off, Tom Sawyer and Huck Finn are classic American figures (as well as a classic DL/MK attraction) based off a classic American novel. I don't care how many kids today know about them (which, from what I've personally seen, many of them actually DO associate with them), Jack Sparrow is NOT a sufficient replacement for them.
POTC has nothing to do with the American frontier, or colonial America. Why would a old-time steamboat be sailing around a tropical island? Are there tropical islands in Missouri, or along the Mississippi River? Were tropical pirate-filled islands common in the American frontier? I don't think so...
There is only so much that can be done with pirates...and what happens when the movie-hype dies down? Frontierland and Liberty Square are both lands dedicated to celebrating American history and heritage, and TSI also acts as a great, quiet, out of the way place to rest in the middle of the day. To see it go away would be very, very sad.
Besides, according to the article, this idea mostly came from Burbank executives who really don't care about theme or story, but rather promoting the latest film and making a quick buck. Perhaps they could 'kind-of' pull it off (i really wouldn't like it though) at DL with NoS, and POTC being right across the river from the island, and a pirate ship (Columbia) sailing around (and their fort also being closed), but this better not happen at MK...