Apple TV as an iOS system wouldn't make very much sense, at least not using the same App Store. TVs aren't touch-sensitive, after all.
*I could imagine a camera as it could be used as an input device for FaceTime or even gesture tracking.
iOS, on the other hand, is designed to run on a few specific devices. The iPad required some work from developers for full support — and that was for a device which still closely resembled the existing iPhone and iPod Touch.