I think he was in no small part a reason for their title last season. I can't remember if it was the first game we played Chelsea this season ....but I remember Luiz being the best player for them. I think Conte is a little like Mourinho in that when he falls out with people he makes reconciliation awkward, hence why Luiz is on the bench but should be starting. He got rid of Costa and hey...I get why, but Costa would have absolutely buried us on more than one occasion if they still had him this season. In fact, I think the entire narrative around them might be very different this season if they still had him.
Luiz is a good passer out of the backline, as athletic as CB's come, and can obviously play in a 3, 4 or 5 so I think we could do a lot worse than sign him, but I will concede he needs to be used properly and play in a system where the individuals know what their roles are otherwise he'll probably look a clown as he has done in the past.