I was always thought 10 million a year would be -disappointing-. The idea it'd sell worse than the 3ds while being the only system they're trying to sell on the market would be pretty bad.
I mean, that'd be roughly in line with the 3DS's first year (I think it did 12 million in its first 12 months?), but without a massive price cut (which meant Nintendo was taking a loss on most of that hardware after the launch period, I believe), with significantly more accessory sales, and with software being sold at higher price points.
Only doing 3DS numbers lifetime would probably be a bit underwhelming, but bear in mind that in the first year especially, matching the 3DS would still mean a better bottom line performance for Nintendo. I think it outdoes 3DS's first year numbers if they can produce enough systems to hit those numbers, though.