Google Now kind of supports this. To activate the assistant thingy, you hold down the home button and press the mic icon. But in the same screen there are also

Google Now kind of supports this. To activate the assistant thingy, you hold down the home button and press the mic icon. But in the same screen there are also suggestions based on what's on the screen (for example, if I'm looking at a forum where someone's talking about an album it'll suggest finding it on Spotify), as well as a plain Google search box.