I wonder if that will do anything to the weight and feel of the controller - cosmetically, it looks identical. Also begs the question of if this will be bundled with Zelda: Skyward Sword.
I expect it will make trivial difference, aside from the convenience of not having to constantly connect and disconnect a Motion Plus.
As for FlingSmash itself... current outlook is meh. There's always been scepticism as to the value of the game, which is reportedly not that complicated and not particularly rich in content.