You'd think it actually wouldn't take that much time, they already have the engine (PH's) to use. All they have to do is create a new country (or re-use Hyrule, again), create a new story (or re-use Ganon, again), add/change some items, think of a fun "gimmick" and some "fresh" dungeons...

Okay, this may be somewhat simplified, but if I got paid to design a new Zelda game I'd have it ready within a month. Seriously, they have more than developement teams to work on: as far we know the capable first part developement that aren't working on anything are EAD, Retro Studios and SPD. As for second party, Alpha Dream is more than capable, and perhaps so are Game Freak and Noise.

Seriously, I see no excuse why Zelda DS 2 hasn't been announced yet.

__________________