The Legend of Zelda: The Wind Waker HD seems aimed at holding over hungry Nintendo fans while it makes a full-fledged sequel, but that's certainly not the only reason for its existence. Director Eiji Aonuma says that the HD revamp is both a product of experimenting for the next Zelda title, and is serving as a test-bed for it.
"When we were thinking about the new Zelda for Wii U, which is something we're actually working on, we needed to experiment with a variety of graphic styles and it was part of that process we took some existing Zelda games and made them HD just to see what would happen," Aonuma told Polygon. "In doing so we realized that the Wind Waker graphic style, the art style, really represented well on the Wii U given the graphic capabilities of the new system. It really brought that world to life. On top of the graphic representation of this world, we were able to tighten those areas I was mentioning before, I really felt like it could breathe new life into this already existing space, this already existing experience."
In addition, Aonuma says it's coming in handy for the future of the franchise, by teaching the team some lessons for the next one. "Not that the sequel will look exactly like Wind Waker, but there are certainly things we can learn in developing for the Wii U," he said.
When the Wii U was announced, Nintendo showed off a brief tech demo of what Link might look like in HD. Aonuma has previously cited Wind Waker HD features like the Tingle Bottle, which ties into the Wii U's Miiverse, as representative of the type of multiplayer ideas they're toying with for the next game.