Someone has spotted some code in iOS 5 Beta that allows for Bluetooth support on 2nd-gen Apple TVs (via 9to5Mac). That doesn't necessarily mean it will be enabled for release. As it is, the device is equipped with a wifi/Bluetooth chip, so the hardware is definitely there.
Adding Bluetooth support would mean that keyboards and mice can be paired with Apple TV. What's also interesting is that this could also mean enhanced games for Apple TV. Bluetooth gaming controllers could be connected to the set-top box, effectively creating a gaming console. If the code is more like what runs on iDevices such as the iPhone, iPad and iPod touch, this could lead to even more possibilities.