That's just pure baseless assumptions though. There is absolutely no proof at all to think that a new Wii Sports or even Wii Fit won't sell extremely well again. It's like saying other consoles are doomed because noone cares about halo/COD/FPS/Uncharted/kinect anymore.
How does playing Wii Sports on a tablet seem appealing to you? People might get REAL sports games instead such as FIFA, Madden NFL, NHL, NBA 2K, MLB: The Show. These actually have an appeal outside of being able to control by moving the remote around.