If you have the $1000 more to spend the 5D3 is great, but if not the 6D is a great alternative. We've been filming around moire issues for years with the 5D2 so saying the 6D isn't usable for shooting video is like saying a new Camry isn't drivable because it only goes just as fast as a Camry from a few years ago and not as fast as a new Lexus.
I've been using the 6D for video since it came out. My clients are happy with the results. Other shooters are constantly blown away by the low-light capabilities. If you absolutely have to shoot moire-inducing patterns regularly, and can't get around it by turning the in-camera sharpening off, tweaking focus, or pointing the camera somewhere else, you obviously know which camera to buy. Otherwise, if you can't figure out how to shoot a good video on the 6D spending the extra grand isn't going to help.
It depends upon what you shoot. If you shoot natural world stuff or outdoors and don't want to have to pick and chose the few things you can shoot the 6D will no way cut it. If all you do it planned studio shoots or planned scenes where you can pick your outdoor background maybe you can get away with it, but that is an entirely different sort of shooting, not everyone does only that sort of shooting.