If the numbers on the front page are right I think 3DS can get to 50M by January 1st, it should have a big next few weeks in sales for sure. I figure it could roll into 49.5M and 50.5M, hopefully on the higher side of my range.
Wii U over Vita is tough for such a short time frame. It eventually will pass it, that's pretty well a given, but I'm not sure. Smash will help the Wii U sell well from now through the holidays, but that is a mountain, especially if the Vita manages any sort of sales over Christmas. I don't think it will be able to reach.