It'll sell whatever Nintendo can produce.  That said, I doubt they produce more that something in the low 20 millions year one, and maybe even less than that (18m? 19m?).

I am sticking with 23m because generally a consoles best performing year is not its first. 

I expect hardware constraints again, so probably no. Without hardware constraints I rather agree.

We learn this info on Sept 29th.

My projections:

~20 million first year from fiirst day of release in any territory.

~2.2 million first CY (2010 - will be Japan only).

~10 million first FY (ends March 31st, 2011).

~28 million first aligned year to date all territories.

@OP:

Surpassing 20M? IF the price isn't too high AND IF you include not only the whole 2011, but also Q4 2010, that is its Japan launch AND IF enough big games are launched during this period, THEN I can agree it's posssible. As I'm sure Nintendo won't screw 3DS launch year for what regards SW, the only relevant IFs remaining are price and including Japan Q4 2010 in the total. All this IMVHO, obviously.

For Japan all 3DS needs is to get its own version of MH3P - MH3P 3D... If that happens (near launch), 3DS Japan sales won't just explode, Nintendo factories will collapse. If I were Nintendo I would work really hard to get Capcom to do that.

That... would be a lot.

3DS will easily beat the DS's first year sales, the DS had PSP to compete with, the 3DS will be the only 3D handheld gaming system on the market, nintendo just needs to price it under $200 and it should sell atleast 20m first year.

 British retailers have stated that 3DS may sell for roughly £150.00, however this is not confirmed and the 3DS' retail price may be higher than that of the DSi XL's original retail price.

I don't think Nintendo is prepared to sell more than 20 million in 12 months and I'm sure this hardware constraints will hurt its sales.