When Ocarina of Time was released, the next game in the series re-used its art design. When Wind Waker was released, it spawned a number of handheld and multiplayer games borrowing its cel-shaded look.
Even Twilight Princess’ art style turned up more than once, even if the second outing was for a crossbow game.
Skyward Sword though, that might be one-and-out. Zelda overseer Eiji Aonuma has told Game Informer:
With Wind Waker, the graphics were suited to handheld gaming. Also the game ended with Link embarking on a journey, so it left open the possibility of what comes after the game. With Skyward Sword, positioning it as the first Zelda game means everything else connects to it and comes after it. It becomes a little bit difficult to do something else within that world and certainly much more difficult to do something that comes before it.
Course, what he could also mean, but won’t say, is that the next main Zelda game will be on Wii U, and with the improvement in hardware will come an ability to display more detailed characters, removing the need for Nintendo to rely on the very basic (if gorgeous) models seen in Skyward Sword.
Which would be a pity! These “simple” Zelda designs have often been the best.