Seems unlikely. Reading their report I'm not sure they're reading the 360 audience at all well. To get that kind of attach rate it needs either a huge upswing in casual buyers - which means a lot of people are going to have to decide to get a 360 and Natal vs Wii, or a heck of a lot of the current install base is going to have to buy Natal.
TBH neither of those seems likely to me. Wii has too much momentum for such as rapid swing to Natal and I don't see the current install base rushing out an buying it in those numbers.
Still, we'll see.
Try to be reasonable... its easier than you think...