From a recent interview with Miyamoto:
[Zelda ST] will be really fun. It’s turning out to be rather challenging. Many of our Japanese customers were introduced to the Zelda series with Phantom Hourglass, and ST could prove to be kind of hard for them, but I thought we’d show them what Zelda is really made of this time around. So it’s turning into quite a unique title.We’ve managed to gather quite a few creative team members for Zelda ST, so I’d like Zelda Wii to also enjoy creative development as much as possible.About MotionPlus. We’re implementing it so that players can feel like they themselves are holding the sword. In the previous Zelda (TP Wii) the targeting was based on the IR pointer. This time however, we’ll be using MotionPlus for a variety of more convenient targeting systems that will allow for more pleasant gameplay.