Boomarang=Magical and Childish
The Boomerang has Australian origins, silly D:. 'Twas not some idea of "magic" or "children", it came from my home ;-;...
Anyway, you're all being silly. Although the Legend of Zelda series has always been predominantly a medieval fantasy in terms of culture, architecture, creatures, landscape and of course, tools and items, the series does throw a lot of other cultural influences into account. Asian, Australia, African and South American, they all appear somewhere throughout the series. For example, the Shiekah are often referred to as a tribe of skilled shadow
ninjas. The Garos from Majora's Mask also had some ninja associated weapons and movements. I could go on, but it's the Ninja that this topic is related to.
Ninjas do appear throughout Zelda, so it wouldn't make too much sense not to find shuriken in on one of the games. The aforementioned Boomerang has an Aboriginal background, but no part of the franchise actually relates to anything Australian. Through this, the shuriken wouldn't at all feel out of place in the Zelda universe. However, from a gameplay standpoint, the shuriken are pathetic. They're just projectiles -- they'd work like arrows, basically. They don't do anything completely different to items you'd already receive. Unless of course, Nintendo found some sort of interesting twist for these items... which is possible. Nintendo do have creative minds, so it's likely that they could find some unique use for shuriken, like firing a certain number at the same time to hit switches that need to be hit simultaneously. Or something.
One more point I'd like to make is that Nintendo do like to throw other cultures into the series. The best example is the Wind Waker -- you were a sailor. 'Nuff said. You took on different cultures other than medieval sword-fighting and horse-riding. In the beginning of Twilight Princess, you were a wrangler and a farmhand... With the risk of becoming too much like Naruto, Nintendo could easily have a game where Link is brought up in more an Asian Hyrule, in which is raised to be a ninja. Sounds silly, of course, but considering the way Nintendo pulled off Wind Waker, I don't doubt that whatever game that uses these cultural influences could still be a Zelda game at heart.
