Google Search added voice control for some system setting, sort of, this past summer. And sort of, meaning, you still had to manually toggle the setting — the app only opened the setting menu for you.
It looks like Google’s finally starting to complete this feature in Lollipop (Android 5.0). However, according to Android Police only three of these commands are currently working: Toggle On/Off Bluetooth, Flashlight, and WiFi.
The ability to turn on flashlight by voice only is awesome.