Future iPad Smart Cases from Apple may have a power connector between the case and the tablet and to provide illuminated notifications. Apple has been granted a patent (number 9,104,371) by the U.S. Patent & Trademark Office for an "integrated visual notification system in an accessory device."
Apple notes that, currently, the Smart Case covers the iPad screen, so there's no visual way for the tablet to provide notifications to the user while the screen protector overlays the display. The case also uses magnetic coupling instead of a power connector.
The patent involves a connector configured to receive electrical power and a control signal between the Smart Case and the iPad. Apple says that, by providing a data and power connection between the tablet and the accessory device, the iPad's processor can "command" illumination elements disposed in Smart Case to be illuminated.
Each of the illumination states can be associated with an operating state of the iPad, allowing the tablet to visually communicate operating state information even while its display is covered. For example, you could see how much battery life remains on the iPad.