I don't think it will happen. It'll be close but the PS3 and Xbox 360 will be able to sell enough that they won't fall that far behind. I don't think Nintendo could do it this holiday season and I expect sales to obviously slow quite a bit for all three consoles and Nintendo won't increase the percentage it has over the HD consoles. In fact, I wouldn't be surprised if the percentage between them narrows slightly.
And I think the PS3 wil become cheaper as Sony will have to lower the price to keep up with and try to catch the 360. I think at the end of this generation, the Wii will have about 45% of the console market with PS3 at 30% and 360 at 25%.
EDIT- The figure of 4 million isn't correct either. It doesn't account for any sales of PS3 or Xbox 360. If somehow those two systems didn't sell at all from this point forward and the Wii added another four million, they would be at 50%. However, since the two systems will of course sell more consoles, the Wii would have to sell well over that amount.
I'll come up with something better eventually...
