although i think ninty actually cant pull this off anyways (vg still isnt big enough, i think the wii might be the catalyst for the next gen), the reason i dont think it will happen is because of production. its not that ninty cant produce that many, but they wont. if they think 1.8 million is still reasonable at this point (which they say is a lot, but they should be thinking much higher at this point) than in no way will it double.
i can understand 30 million in 2008 as a high prediction, but anything above that isnt possible due to ninty themselves.