I don't think they should go for a "realistic" look. I prefer toon shading as it more closely resembles painting which looks more like the way we see than some crap overdone graphics game like Ninja Geiden with bland backgrounds, uninspired character designs, and overtly crisp textures even at a distance. Realism is a trend like 3d is a trend. Realism actually doesn't look real, it looks unprofesional. WW looks very real because of its consistencies not only within the game but the consistencies between the game and the atmospheric effects found in reality. WW flat shades of light/dark and color to simulate what has been done in past toons, but those toons simulate the classical traditions of oil and water painting. Realistic games as they call them are defined by thier "realistic" approach to textures and bumpmapping. The problem is that in reality you can't see any of that crap. In reality you see flat shapes with varying size and value.
So in closing I support the continuation of cel shaded gaming in the Zelda franchise, but I feel that even though WW had the greatest character and background designs of any game ever I think they should change the design style to a more naturalistic or manuristic style instead of a manga style as found in WW. Also themes, story, sound, voice acting, cut scenes, emotion, deaths (maybe), and other things would really benifit from a maturation. Difficulty should increase and my own personal complaint of course is that the adventure in WW was so overplayed, straight forward, linear, old, and lacking ambition. The ocean should have had continents as well as some small islands. Instead it was a grid with a ton of little islands and never a grid of just open ocean.
In a realistic Zelda I would have Link ride a dragon that eventually can swim and fly as he grows as well as run fast and attack enemies while you ride.