So yeah 3DS is a pretty big news, one that is usually worthy of an E3 show. One would ask himself why the big N decided to drop the news now, in march, just a few days before the end of the fiscal year....

Evidently there are negative effects to a new console being announced. First, the old console will seem obsolete to the advised customer, and Nintendo is barely releasing the XL in europe, so it makes little sense to not even let this one fly a little... afterall, anouncing the console now rather than E3 does remove a few months of sales.

Secondly, as we have seen in the past, releasing a product with a new tech will make the competition revise their plans so that they are not completely taken by surprise if it succeed (think sixaxis... though that didn't quite work)... and this is even more the case if you are the first one to present your product. Now with sony already talking about 3D for a few months, do they really have a choice not to include 3D in their next handheld? or at least to heavily weigh the option?...

so these are the negative points... but what are the advantages?

Well considering they plan a late 2010/ early 2011 release, at least for Japan, one could assume that they would want the public not to feel betrayed with a sneak release. The console will be retro compatible, which is good for continuity and thus developpers will still maintain production for the DS. Also, announcing this one year before the release will increase the initial sales as people will hold off buying current gen material if there is a next gen just arround the corner.

One other important point I believe is the public image one, and this point strikes on two levels. Firstly, Sony has had a lot of news recently with the move, and although there are the differences with the Wiimote, Nintendo (and most specialy Reg) does not seem happy of all the enthusiasm that is gathering arround the move. Afterall, the wii was pointed as a gimick by the press and attacked for the past 3 years, but suddently since the PS3 is the console getting motion control, it's became the new holy grail... As much as reviewers are biased, they still have some weight on the general market and if they only talk of the moven this is bad for nintendo. So a release of a new Nintendo console, with just a few details will bring the focus back to the big N. Who cares about accessories for last gen when a new gen handheld is there (sure console and handhelds are not the same gen, but you get the point)? So this first point is disruption of the current momentum that was against nintendo.

The second point relating to the public image is directly in relations to the 3D. Since console gamers have no clue that 3D gaming exists quite well on PC and since the general crowd is still in awe from avatar, Sony had the nice idea of claiming 3D as a sales argument. Off course, you can't even play any 3D games yet and still for a while to come (and even then you'll need an expensive setup), but the argument of PS3 3D still resonates well to the ears of the general crowd... well it seems sony was not the only one interested in the developpment of 3D as Nintendo has a handheld playable for E3... and what does announcing this now do? well it just takes away all the awe sony was trying to create and brings it to the future Nintendo handheld. So now that people are pumped for 3D... where are they most likely to be able to play it? not on the 3000$ sony 3D tv, but on the 200$ nintendo handheld comming out in less than a year too... with full developper support non the less.

So in all, the reasons nintendo announced it now rather than wait is because it both takes the media back to their pockets, and secures the global interest for 3D as a Nintendo thing (for the mass market that cannot spend 3000 on a new TV just for gaming).

And about stealing E3... well there are bound to be quite a few 3DS games to be shown, that will have the exact same effect than if the console wasn't announced before... the anouncement was really for media buzz and attention.

(just felt like writting a booring piece, goodnight!)

Pro: Get's people excited.
Allows people to contact Nintendo for suggestions.
Nintendo first to announce 3D handheld.
Some other stuff I don't really care about posting.

Cons:
Early announcement of new DS will lower sales of the DS's currently on the market.

Looks like you got most of it taken care of...

Considering most people who know about the 3DS probably already own a DS anyway, I doubt it will effect sales too much.

The reason Nintendo releases new hardware is when their old hardware can no longer sell software. AS shown by the recent Zelda release software sales are definitely in decline, so while they could drag out the DS for another 3-4 years and sell 200+ million units, they would rather release a new system and reinvigorate software sales. The Ds has done it's job and really, the only reason to keep it on the market now is for the glory of having the most popular video game system ever released.

That's the point. By announcing one particular feature now, they will force Sony to quickly implement it, so that Sony might release an otherwise rushed product. 

After that, Nintendo can just announce their other features that will make it sell.