Will Wii Fit Plus make it? Well, it could easily be compared to Wii Fit from last year.
Wii Fit + looks to be selling slightly more than Wii Fit did in the equivalent time-period last year, in Americas. From here till the Week ending 3rd January, Wii Fit sold 1.1 million, Wii Fit + thus looks at 1.1-1.4 million, or so.
Roughly the same seems to be the case in Others, were Wii Fit + has sold pretty much 250K each week for the last 5 weeks. That's more than Wii Fit did, as it ranged from 150-210K in that period. Wii Fit sold nearly 1.3 million here, so 1.3-1.6 million seems a likely number for Wii Fit Plus.
Wii Fit Plus should also rack in 300-400K in Japan.
That leads to 2.7-3.4 million expected for the next month. That puts Wii Fit's total at 6.3-7 million.
Thus, Wii Fit Plus needs 3-3.7 million.
If we (yet again) go look at Wii Fit, it sold 4.1 million in Q1 2009. Keep in mind that at this time, Wii Fit had been out for over 6 months.
Wii Fit Plus looks to have a stronger holiday, and it's also a newer game than Wii Fit was. It should manage to sell 3.5 million +.
All in all, I think Wii Fit + will sell 10 million by the end of Q1 2010, whereas Iwata was most likely talking shipped.