I appreciate the fact that the AirPlay icon automatically lights up when I walk into my abode and get within range of Apple TV. But I bet a lot more people beam stuff to their big screen if Siri got involved, and she knew where to fetch the content. "Hey, Siri, play the trailer for 'Dark Knight Rises' on Apple TV" Or how about "Play slideshow from Jake's birthday with my Party mix on Apple TV."
In the first instance, Siri would know to grab the clip from YouTube, start playing it and stream it to your big screen. And in the second example, she'd be intelligent enough to open the appropriate photo gallery and then set it to the correct iTunes playlist on your HDTV. Hey, it could happen.