Correct me if I am wrong but not even the 997S has an LSD unless you pick the sports suspension (-20mm) and LSD pack which comes at no charge. I am sure that it would be an improvement in the track as it is for the 911 but it could make the car harder to drive for the average driver and given the power and traction of the car it is not vital...

As for whether Porsche needs to go Mid-Engined, yes and no. All the mid-engined samples they have made are great cars but still the Rear engined rear powered cars offer such massive traction and are so rewarding to drive that I wouldn't feel right seing porsche without RR 911s.