Sony' Wand isn't a threat at all. seeing how successful and mainstream the Wii is, Sony's Wand will always be seen as just a Wiimote ripoff. not to mention the thing doesn't even have a nunchuk, you need an entire controller in your left hand to play with it.
Natal on the other hand could become a threat if it works out for MS. as Natal and Wii's controls are completely different.