I believe it is too soon to make a good estimation. But we can still try.
Let's look at the hardware first. What we know about the 3DS: glassless 3D; it's backward compatible with the DS line; it has a motion sensor and a gyro sensor. Unknowns: price; battery life(it was stated that they want it to be similar to the DSi's)
Comparing it to the DS it has more control methods, which could lead to some interesting game ideas. Being compatible with the DS I expect that this will help DS users move to the 3DS, especially those that only own a DS phat.
However, we must not forget that the most important part of a game-console, the games. Let's get the 3rd party games out of the way first. The 3DS has a lot of 3rd party games announced, much better than the DS had when it was launched.
While 3rd party support will move hardware, like all Nintendo platforms it's the 1st and 2nd party games that will truly push the system. So the announced games from Nintendo are:
Animal Crossing
Kid Icarus: Uprising
The Legend of Zelda: Ocarina of Time 3D (port/remake)
Mario Kart
nintendogs cats
Paper Mario
PilotWings Resort
Star Fox 64 3D (port/remake)
Steel Diver (new IP)
Before I start discussing about them, I'd like to mention that at the moment the 3DS is being downplayed for having a lot of ports. We do not have info for the majority of 3DS titles, about the ones we do know most of them are new games. Also people have forgotten that the GBA, DS and PSP were launched with ports of console games. In fact Nintendo released only 1 game when the DS was launched in North America: Super Mario 64 DS.
One more thing, none of these announced games from Nintendo are for the expanded audience. Before you all tell me that nintendogs cats is, Nintendogs and Brain Training were expanded audience games on the DS, on the 3DS these games are for the core audience. So Nintendo will need something new to get new gamers. However, I feel that I need to remind people that on the DS the expanded audience games were released a while after the hardware was released.
Animal Crossing, Mario Kart, and nintendogs cats are sequels to games that sold a lot on the DS. All three of these games have high chances of selling over 10 million units, and they will push hardware. The least is known about Mario Kart, from the images there will be racetracks from Wuhu Island. Animal Crossing will have the player take on the role of the town mayor, while nintendogs cats will have, besides the introduction of cats, the animals react to the players movement via the camera as new things compared to the first.
The Legend of Zelda: Ocarina of Time 3D, Star Fox 64 3D, and Paper Mario will sell mostly to long time Nintendo fans. I think that they will push hardware but not on the scale of the three games above.
Kid Icarus: Uprising and PilotWings Resort can be considered new IPs, seeing as how long it has passed since the last games. It also means that I have no clue how much they will push hardware. PilotWings Resort is set in Wuhu Island, it would be interesting if you could import Miis from your Wii. More info is needed.
And finally Steel Diver, I don't think it will move hardware to be honest. It might pass a million units. I have to say that we do not know how many of the games announced will be released when the 3DS launches.
At the moment Nintendo seems to be trying to get DS users to upgrade and to steal some PSP owners from Sony, I expect that the big N is trying everything to get a Monster Hunter game on the 3DS.
All things considered I believe the 3DS can sell 16 million units in its first 12 months. I need more info to predict after that, it depends on what games Nintendo will bring.
