This has been discussed many times on here. Personally I am strongly against it. For one thing I am not a fan of playing players out of position, especially in the DM role since mistakes there tend to be more costly than anywhere else. As for Luiz's attacking abilities, I feel that he is now able to contribute to the attack because he plays at CB. If you move him to the middle, he will not have any time on the ball, he will have a player marking him which prevents him from going forward effectively, and he will also be needed to pick out a pass quickly.