The David Luiz to Barcelona thing is going to be talked about until the Catalans acquire a new centre half, but the chase isn't going well for the defending La Liga champions, mostly because negotiating with someone who doesn't want to sell and has all the leverage is notoriously difficult.
The problem is not whether he wants to come, but that in the end you have to get away from Mourinho -- and that is not going to be easy. The idea of facilitating David Luiz coming to Barca would not pass through his head, and even less if it is to strengthen us. It is more than difficult for us, almost impossible.
-Source: El Mundo Deportivo, translated by ESPN.
The thing about having players signed to four-year deals is that there's zero incentive to sell them if the club doesn't want to. Some people don't like this (there was plenty of whining about Tottenham Hotspur not selling Luka Modric under similar conditions a few seasons ago), but it's a simple economic fact and part of the reasons players get paid so much money. Contracts matter, and if Chelsea don't want to sell David Luiz, they won't sell him. At least Dani Alves is being sensible about it.