Eh, post again?
Nintendo Japan website has a 9 minute video of Iwata apologizing for the stock problems for AC, and explaining why/offering alternatives (download version).
http://www.nintendo.co.jp/3ds/egdj/info/movie.html
Basically, the game requires a larger space for save data than any other 3DS game, and needs to use a special type of ROM (SLC-NAND) to save the data to quickly. It's more expensive than MLC-NAND (which is used by all other 3DS games), faster and lasts a lot longer (about 10-20x as many writes). It's because the game uses this type of ROM that they can't just use cartridges from other games.
Problems with creating these cartridges may also have a hand in AC not being available worldwide; they can't even create enough for Japan let alone other regions.
Basically, I wouldn't count on a date for AC just yet.