I think they could've done alot more on the current Wii though if they wanted to, you have things like Morrowind and the GTA's on consoles last gen. It doesn't really get much more expansive than those.
Besides, I'm not saying they're going to make an open world zelda game. I doubt that very much. I just think we're going to see much larger areas with much more intricate detail, large sprawling SotC style bosses, and overall much more cinematic and epic moment with the next zelda.