For some, this will be the worst news ever. For others it'll come out to no more than a shoulder shrug. I'm somewhere there in the middle.
Those hoping to import Japanese games for their US Nintendo 3DS are out of luck. Those wanting to play imports will have to buy a foreign system as a 3DS from one territory will not play games from another. Hell, it won't even 'see' the games.
As you'll see in the above video, a North American copy of Super Monkey Ball 3D will not even register in my Japanese 3DS' menu. An empty slot is shown, just as if nothing was inserted. Popping it out and replacing it with a Japanese game, you'll see the game's icon come up, no problem. I think it's pretty safe to assume that things will work the same for US 3DS systems and Japanese games. Nintendo has this system locked down!
For me it's not so much of an issue. I already have a North America 3DS reserved as I need it for work. Avid importers will likely want to own a foreign system as well. But I'd bet that many other gamers looking to import a game or two will be disappointed.
Note that your imported DS games will still work fine, as we reported in our 3DS Q&A article.