I'm not sure of my opinion right now.
To me, TSI doesn't have much emotional meaning, I've probably been there once or twice as a kid and have no real connection to any of it, no memories, nothing.
But a pirates overlay, as much as I love pirates, just doesn't feel right. As many others said it would really throw off a lot of the surronding themeing. Why would a riverboat be circling a tropical pirate island? Why is this tropical pirate island surronded by this thing called "Rivers of America", etc.
I think I'd rather see some TLC given to the island, revamp the play areas, take the interaction ideas from the pirates idea and incorporate it in a way that will befit the era. You can stray away from the actual idea of Huck Finn, Tom Sawyer, and Mark Twain while style keeping it in the time period and interesting to even those young ones who don't know who Mark Twain and his characters are.